Our history is white washed to a degree...but the Columbus bit is exaggerated. Columbus himself did not kill many native Americans, though it is popular to accuse him of killing off the Indians [or to blame other white men for it].
The real killer was Disease. 90%+ of the Native-Americans were killed by disease, and there was no way to prevent that. That is not anyone's fault. Even today, isolated tribes in Brazil that have had 0 contact with people outside of thier tribe for centuries, get nearly wiped out once they make contact with westerners for the first time...They have 0 immunity to most diseases from Africa, Europe and Asia.
Its PC to say Columbus was a bad man and killed the Indians off, but its not true. And your claim of Columbus killing 90% of the Indians is the PC garbage...disease did that. You cant say that if 90% of a population died by Small pox that it was Columbus's personal fault. No one even knew of Germs or microbes in those days.
And the diseases Columbus and other Europeans brought with them [unknowingly] spread to North America and S.America pretty quickly...Its common for our history books today to state that the English literally stole land from the Natives in the US [and butchered the natives]...But there were not many people living in the Eastern US at all by the time the colonies were founded. There are tons of English accounts stating abandoned native villages, to them the land appeared largely uninhabited [with extremely small numbers of natives spread out over large distances]. Diseases wiped them out before the English even considered forming colonies in the US.
You should read the Zinn chapter I'm talking about.
You're right that disease was a huge killer that was mostly unintentional.
But you're wrong on many counts. For example, from the moment Columbus met the natives. His own diary says how the first meeting went - the natives were warm and friendly, rushing to meet the ships and people and treat them well, I think there were gifts; Columbus on the other hand, had his men show the natives steel swords to see if they were familiar with them, and seeing they weren't, estimated it would not take many armed Spaniards to put all the natives into subjugation.
If you're broadening the topic to North America, disease killed many - but was not the issue in massive campaigns of burning native villages, men women and children, shooting any who ran away from the fires, and other such genocide. Disease does not make the real history 'PC' or 'false', it's just one part of the story that goes alongside the rest.
See my anecdote about Columbus's successors who wanted there to be gold so much they forced the natives to find the non-existent gold or be killed.