Anyone is free to oppose everything about American society and culture, this includes history. They may be hypocrites or a glutton for despair, but it's completely ok in the eyes of the constitution. As long as there are no laws broke, then it's part of expression.

There are plenty of anit-Americans who are living here.

For you to say that you don't like it is all fine and good. To want or hope that something happens that makes them do something different, that they don't want to do, could be construed as anti-American as well.