"acceptable to have differing political opinions" is not the same thing as "all political opinions were acceptable". The former was true, and still is. The later never was true, and never will be. But supporters of deeply unpopular opinions always try to pretend those two things are the same.
What are you talking about? The US was founded by getting people out into the streets and countryside to fight over politics. The Civil War was a fight over politics (the politics of slavery for the South where they wanted to keep it legal). The US has constantly had fights, actual violent fights with many deaths, over politics. It isn't something that just started after you were born.
Politics is how we interact with each other as a group, how we make decisions as a society and put those decisions into effect. That seems like one of the least stupid things I can think of.
> wasn't like that before my time
As the great William Martin Joel once said, "We didn't start the fire. It was always burning, since the world's been turning."
You haven't done much reading about history, did you?