In the end, they're like the tattoos that someone else commented on. (I have those as well.) If you appreciate them, great! If you don't like them, that's fine too. Fundamentally, they're not for you.
Remember when who you voted for was sacred knowledge?
I think you might be romanticizing this, a bit. When you convince the public that not talking about something is the best course of action, they become a lot easier to control. We learned this during WWII with the propaganda machine that was fully employed on all fronts, and arguably before that with the work of Edward Bernays and people like him. If public discourse and debate could be quashed, then it was much, much easier to simply tell everyone what their opinions of a thing should be.
I think the big difference now is that people have a megaphone in the form of social media and they forget just how wide the statements they shout through it can spread.
What is a problem is doing it on an environment where participation is mandatory or required for basic survival.
A good portion of these stickers are to do with things that are political or quasi political. What tends to happen is that a lot if times people have been burned in someway for supporting an idea or a cause. This is often because people have been fooled by charlatan, or it was later revealed that things were more complicated or different than they were led to believe.
Cringe and why people hate it is best explained by watching the very first episode of the UK office.
Most people want to go to work, turn up and do their time and go home. People that are often top enthusiastic are difficult to deal with day to day. People that adorn their personal possessions with slogans are seen as a warning sign.