I would say it's a type of strawman fallacy.
It’s much easier to defeat your opponent’s argument when it’s made of straw. The Strawman argument is aptly named after a harmless, lifeless, scarecrow. In the strawman argument, someone attacks a position the opponent doesn’t really hold. Instead of contending with the actual argument, he or she attacks the equivalent of a lifeless bundle of straw, an easily defeated effigy, which the opponent never intended upon defending anyway.
In example 1, the response claims that violence would happen anyway, so it's apparently "just fine" for it to happen that way, "since it was going to happen one way or another".
Argument: "The US government engaged in a targeted and precise campaign to destroy Native American culture, including warfare and removal."
Rebuttal: "Native Americans were fighting each other before white people even got here. Humans have been fighting each other from the beginning of time."
Incidentally, I've heard this kind of argument used against racial violence.
Why should we bother with preventing white-on-black violence when black-on-black violence exists?
Personally, I'd counter with:
Why bother with preventing black-on-white violence when white-on-white violence exists?
But I'm pretty sure the people against BLM wouldn't understand the logic of using their own lack of logic against them. But I digress.
In example 3, it's assuming that it doesn't matter that taking land and resources from someone is OK, because they aren't the original owners of it from the beginning of time.
Argument: "Native Americans land was taken from them by force and deceit."
Rebuttal: "Native Americans aren't native. They came to the Americas from somewhere else just like the rest of us."
For example 2, I'd think of that as a hasty generalization.
A hasty generalization is a general statement without sufficient evidence to support it. A hasty generalization is made out of a rush to have a conclusion, leading the arguer to commit some sort of illicit assumption, stereotyping, unwarranted conclusion, overstatement, or exaggeration.
By stating that "everyone else is doing it", it ignores those who don't do it as well as not including anything to support their statement. Even if they could somehow support their statement, it would be fairly easy to disprove the statement by showing how corporations don't all lobby and how some politicians don't take lobby money.
Argument: "X corporation's lobbyist's leverage their wealth to influence Y politician."
Rebuttal: "That sounds like all corporations and politicians."
It could also be a strawman argument, since it's trying to remove the validity of the original statement. They are trying to spread blame, which actually doesn't invalidate the original statement as they want it to. In trying to spread blame, they are attacking something "the opponent never intended upon defending anyway."