That's everyday silly.
Even before white colonized the Americas, the natives were killing each other and enslaving other tribes. I prefer that version of the natives of the stereotypical liberal version where natives are portrayed as peace lovers who smoked weed and were about peace. The same holds true for Africa where Africans traded captives from other tribes to the Europeans in exchange for gold, food, guns, clothes, etc.
But they weren't that violent really at all. The biggest source of Native American violence was on the east coast and south-eastern region of North America, where you had big farming societies that would get raided by other tribes. But that's only part of the millions of natives living all over the Americas.
In comparison, Columbus would cut off native's hands, sell them into slavery, turn their women into prostitutes for his soldiers, and he set in motion a centuries-long genocide where basically all of the native population would be killed off at some point. This is one of the few appropriate instances on the internet where I can say that you're essentially arguing for something on the same level as saying, "Well,
some of the Jews killed in WWII were probably violent criminals!". Not Godwin's Law.
edit: oh god there's more
As far as diseases go, no one knew why people got sick or how they spread. To the Europeans if someone got sick, they thought they had been cursed by god or their blood was bad. They weren't forced on to the natives, but because of frequent contact they ended up getting easier spread. At the same time, the colonials received diseases that they had not encountered before.
We have actual letters dating back from the 1760s that show instances where Native Americans were deliberately infected with smallpox in order to wipe out their communities. Also, give me one example of a
serious illness the colonists received from the Native Americans.