Answer: This is not a fact and can be seen under close scrutiny. Many atheist sites utilize the scholarship that assert Jesus Christ never existed as a real, historical figure. Those who would teach such a thing are ignoring much of the historical data that is available concerning the time of Christ.
The "so-called" history and sayings of Jesus are indeed authentic and this is clearly demonstrated based on what we know about the scriptures and how they stack up against other literary works of antiquity.
The idea/theory that Jesus is not actually a historical figure, and was derived from mythical "savior-god" stories of antiquity, has been circulating among atheists for a while now. They cite the same old sources for each article/book they produce. In the case of the deities that you mention, Gerald Massey, Geoffrey Higgins and Barbara Walker are the sources that are used for the most part. There are currently (that I am aware of) NO original citations from Egyptian/Indian records/sources.
First of all, Christianity does not need any outside influences to derive any of its doctrines. All the doctrines of Christianity exists in the Old Testament where we can see the prophetic teachings of Jesus as the son of God (Zech. 12:10), born of a virgin (Isaiah 7:14), was crucified (Psalm 22), the blood atonement (Lev. 17:11), rose from the dead (Psalm 16:10), and salvation by faith (Hab. 2:4). Also, the writers of the gospels were eyewitnesses (or directed by eyewitnesses as were Mark and Luke) who accurately represented the life of Christ. So, what they did was write what Jesus taught as well as record the events of His life, death, and resurrection. In other words, they recorded history, actual events and had no need of fabrication or borrowing. 
There will undoubtedly be similarities in religious themes given the agrarian culture. Remember, an agriculturally based society, as was the people of the ancient Mediterranean area, will undoubtedly develop theological themes based upon observable events, i.e., the life, death, and seeming resurrection of life found in crops, in cattle, and in human life. It would only be natural for similar themes to unfold since they are observed in nature and since people created gods related to nature. But, any reading of the Old Testament results in observing the intrusion of God into Jewish history as is recorded in miracles and prophetic utterances. Add to that the incredible archaeological evidence verifying Old Testament cities and events and you have a document based on historical fact instead of mythical fabrication. Furthermore, it is from these Old Testament writings that the New Testament themes were developed.
In addition to the above, there are other compelling reasons to reject the notion that Christianity was simply "lifted" from pagan sources:
Due to space limitations, let's a look at one of the myths you mentioned in your question (Krishna of India). I am taking the list of "similarities" from a popular online skeptic, Arachaya S., whom you are likely familiar with.
Let's see how the similarities appear under closer scrutiny (note: this is certainly not a scholarly, exhaustive examination of this subject, I am just a layperson, however J.P. Holding of Tektonics.org in my opinion is unmatched concerning this Jesus/pagan/copycat myth topic):
||Krishna was born of the Virgin Devaki ("Divine One")||It is true that Krishna was (born of hairs from the head of Vishnu which that god placed in her womb), 
however, this is in no way similar to the virgin birth of Christ for three reasons:
|His father was a carpenter||Krishna's father was named Vasudeva. His occupation was not mentioned in four separate sources that I researched. If there is a solid source (preferably one that is neutral to the Christ as Krishna issue) that indicates Vasudeva was indeed a carpenter by trade I would like to know about it.||His birth was attended by angels, wise men and shepherds, and he was presented with gold, frankincense and myrrh||None of the sources I have consulted have detailed such explicit gifts offered, only that there was great celebration at Krishna's birth.||He was persecuted by a tyrant who ordered the slaughter of thousands of infants||Kamsa or Kansa, Devaki's brother, decided to destroy all the children (not infants) in the region who were rather unusual (not because Krishna was thought to be the promised Messiah as Herod did). Additionally, this slaughter was done out of fear for his [Kamsa's] own life as an oracle prophesied to him before that one of Devaki's nephews wanted to kill him. Moreover, the slaughter of the innocents by Herod was a historical fact of history.||He was of royal descent||Yes, he was considered to be royalty, but there were so many myths and even historical data recording a number of royal births as to render this comparison meaningless...||He was baptized in the River Ganges||Here is a "borrowing" again of Christian terminology to describe this event. Krishna was NOT baptized in the River Ganges. Funny thing is in ALL of the versions of the narratives of the Mahabharata that I consulted, this term was NEVER used in relation to Krishna.||He worked miracles and wonders.||So what? I mean really, the relationship between mythological characters and supernatural powers, miracles and wonders is a common one. Not only in Indian myths, but Greek and Egyptian.||He raised the dead and healed lepers, the deaf and the blind||Again, based on my source material, I am skeptical about these specific terms, however for arguments sake if Krishna did do these things, see above.||Krishna used parables to teach the people about charity and love.||Again, this is not significant. Many teachers used illustrative stories. Also, I am noting again, the convenient use of the word "parable" to sway the casual reader.||He lived poor and he loved the poor||Suffice it to say that this is a bit of a stretch isn't it? How many poor heroes or heroine can be plucked out of stories/myths/narratives of antiquity? Quite a few I am guessing. This means nothing.||He was transfigured in front of his disciples||Again, use of New Testament language (transfigured and disciples) in order to indicate similarities to the casual reader... There was a definite difference between the Transfiguration of Jesus and this revelation of divinity from Krishna. Jesus' transfiguration again, is a fulfillment of Old Testament prophecy: Is. 42:1 “Here is my servant, whom I uphold, my chosen one in whom I delight; I will put my Spirit on him and he will bring justice to the nations. Again, no reason for a devout Jew, well-schooled in the Hebrew scriptures, to borrow from pagan literature when recording the transfiguration of Christ. Quote taken from the Mahabharata: “Krishna laughed and as he did, his body suddenly flashed like lightning. He began to grow in size and various gods issued from him. Brahma sprang from his forehead and Shiva from his chest” (KD 492). [Krishna allows even the blind Dhritarashtra to see his glory.] This animated version of Krishna growing in size and having gods pop out of him is typical of the mythical narratives, but does not resemble the biblical record of Jesus which:
||In some traditions he died on a tree or was crucified between two thieves||This is untrue and there is a KEY quote from a MAJOR skeptic/unbeliever that I want to use here: "In fairness, however, one purported similarity needs to be discredited. Skeptics sometimes cite Kersey Graves in Sixteen Crucified Saviors or Godfrey Higgin's Anacalypsis (which Graves drew from) in asserting that Krishna was a crucified deity. No such event occurred in the Gita or in any recognized Hindu scripture. Given the pronounced syncretic tendency of Hinduism, it is safe to assume that any odd tales of Krishna's being crucified arose only after the existence of Christian proselytism, in imitation of the Christian narrative. It is neither authentic to Hinduism nor is Hinduism the source of that portion of the Christian narrative. The same may be said for most of the purported nativity stories. In my opinion, both Higgins and Graves are highly unreliable sources and should be ignored."
It should be noted that Achayra S. has quoted HEAVILY from the aformentioned sources to develop this list citing alleged similarities between Krishna and Christ! What is the motivation of the author here since he is obviously not a Christian and apparently does not agree that Christ existed? I think we can conclude that he is not biased towards the Christian position and is simply reporting the facts as he has observed them.
|He rose from the dead and ascended to heaven||According to the quote above, it appears that this "similarity" arose after the existence of Christian proselytism. If Krishna wasn't crucified and the story is not authentic to Hinduism, then it could follow that any (NT terminology again) "resurrection" and "ascension" would be as well.||Krishna is called the "Shepherd God" and "Lord of lords," and was considered "the Redeemer, Firstborn, Sin Bearer, Liberator, Universal Word"||Blavatsky, Walker, Graves are cited by Arachaya S in her work Origins of Christianity (again, where the list to the left comes directly from) and I think more than sufficient doubt should be cast upon a Graves citation... ||He is the second person of the Trinity, and proclaimed himself the "Resurrection" and the "way to the Father.||Graves citation. see above.||He was considered the "Beginning, the Middle and the End," ("Alpha and Omega"), as well as being omniscient, omnipresent and omnipotent||Graves citation. see above.||His disciples bestowed upon him the title "Jezeus," meaning "pure essence"||This does not parallel the New Testament narratives about JESUS. Ignoring the New Testament term of disciples that has been again borrowed for effect, the disciples did NOT bestow Jesus' title to Him. The name Jesus is a transliteration of the Greek form of the Hebrew name Joshua. The meaning of the Hebrew name is “Yahweh is salvation.” The name was chosen by God and communicated to Joseph and Mary by an angel. Matthew 1:21.||Krishna is to return to do battle with the "Prince of Evil," who will desolate the earth||Again, this similarity is not significant enough to even deal with, especially now, after seeing the utter dishonesty shown in presenting these points of "likeness" between Jesus and Krishna.|