Humanity has bad spots and problems everywhere. Here in the US we throw the expression "greatest country" at the drop of a hat. What is greatness, if not to try to work on our problems as much or better than everyone else is working on theirs?
People that want to wallpaper over our history of mistakes are doing the opposite of making the country great. True greatness is recognizing the problems and working hard to fix them. People like Sanders are the opposite of patriots. She would have us lie about who we are and what we've done, perpetuate our mistakes, and oppose those that want to do the work to actually make us greater.
Lemmy is a bit of a darkweb corner. It's growing fast from Reddit users, but redditors are not particularly known for being the best form of the online argument either.
Like anywhere else, I'd say pick your communities carefully. And accept that a platform that is in shift and growth has a lot of potential for weird encounters. Try not to take the bad experiences too personally.