The people around today may not have directly committed those acts, but they benefited from them in a million ways, even today. They have the stuff that was taken. They have the money from extorted labor, or the things that were bought with it. They have a society that was built to privilege their interests at the costs of others. None of that belongs to them - it never did. For that sort of thing to be taken away and given to the people who it rightfully belongs to is just plain justice.
Second of all, this isn’t something that happened in the distant past. The legacy of it affects people today, constantly, and will continue to do so in the future. People are systematically disadvantaged by these systems that still exist in numerous ways embedded into the structure of society. They get treated differently. They lack the resources that they would have otherwise had, because the generational wealth that by rights belonged to their families was taken and given to someone else instead, so they didn’t have the opportunities that growing up with those resources brings.
Have you ever seen an article about some young person who has had some incongruous success in, I dunno, real estate investment or Fungible DogeBit or whatever? They always have the same sentence in there, somewhere, that oh, they got some starting money or favor from a parent or family member. So they had starting capital, a better education, more connections to people in power. People in disadvantaged groups don’t have those things, and consequently they don’t have the opportunities that those things provide. This is a continuing injustice, it affects people today and it will affect people in fifty years, a hundred years from now unless someone does something about it, gives people back what was taken from them, so they get to have the opportunities that those things provide.
Third, “How do you address the treatment of the native Americans? You can't give the land back.” Yes you can. Maybe it would be inconvenient, have practical difficulties, but you know what? “Oh, I can’t give back the stuff I stole from you, because that would be a big hassle to me. Haha sorry lol.” is bullshit. It could be done, surprisingly easily, if people actually were willing to do so.
