If you talk about America in any negative light it's always assumed to be relevant to the election, and they feel obligated to interject with, "this is how you get Trump" at any opportunity. To accept criticism of America they need to make sure this phrase stating the obvious is included somewhere: "Democrats may be bad sure, but they're clearly better than Trump." Unless you express that specific sentiment you're assumed to either be an idiot or helping Trump get elected. Always very touchy when it comes to their asinine politics and obsessed with making sure everyone agrees with them or you're their worst enemy.
It doesn’t help that the “both sides are bad” argument is commonly used by right wing trolls. Lots of liberals have the immediate reaction to get defensive because they’ve seen how quickly the “ugh this specific thing I don’t like sucks” argument devolves into “nothing has changed with Joe so it doesn’t make a difference,” which leads into “might as well not vote at all, or vote red because it doesn’t make a difference.”
Just the phrase "both sides" on it's own can get this ridiculous charade going. Both sides are political parties in the US, both sides further America's geopolitical interests, both sides are largely financed by corporate donors who donate to both parties, both sides are economically right wing, both sides engage and amp up the post-political partisan spectacle. "HEY THIS RUSSIAN TROLL SAID THE BAD WORDS!"