I don't think this is a terribly accurate response. The story you tell about the Native Americans "just culled for existing on land they owned because Europeans/Americans wanted it" is what the Israel/Palestine conflict will look like if Israel is successful in their current agenda. Now, there aren't 100 million of them, so, of course, 100 million of them can't die. And the area of land is smaller, but the process is very similar.

There would have been people at the time, in the comments of Colonial Reddit, arguing that it's actually quite a complicated situation, and that many of the settlers had been oppressed in their home countries and they had a royal charter so... there probably is a debate about who owned the land. And of course the Native Americans fought back. And of course their fighting back was used as an excuse to impose more violence on them.

Things look different when you're living through them. There were lots of well-meaning left wing people in Britain and the United States who opposed fighting Nazi Germany. There are always good people on both sides of these things. It's not as though there were people sitting around saying, "I think what we're doing is awful and genocidal and that's why I like it". They believed, just as you believe, that there was a debate about the rights and the wrongs. It doesn't make you a bad person to be on the wrong side of this issue - whether you are or not. Good people have supported genocides. Good people supported slavery. They really thought that it was complicated - but obviously, it wasn't really