There are some rather unhinged people on the left, sure, but they're basically just nutters on the internet, maybe a few activist groups, and things like that. They're certainly not the ones running the show: by and large the people elected to office on a Democratic ticket are ... just normal sane people.[1] People you can disagree with, dislike, or even hate: that's all fine. I intently dislike Ronald Reagan, but he was also a relatively normal sane person so that's okay, and part of the normal democratic process.
What we've seen in the Republican party is completely different. Not just over the last few months, over the last few decades. Remember Mitch McConnell just outright obstructed anything for years simply as a power game to make the Democrats look bad? Or Republican actors cooking up crazy conspiracies about the Clintons and then banging on and on and on about it for years and years?
And of course the Democratic party isn't perfect. But there are degrees of things, and it's just not comparable. This is "murder, rape, and shoplifting" – all are illegal and should be prosecuted, but they're also not hte same.
People saying that "both sides are the same" are deeply and profoundly misinformed, suffering from pseudo-intellectual delusions of "being above it all", or just outright arguing in bad faith.
[1]: I'm sure there are the occasional exceptions – there are thousands of people if we count federal, state, and local level and any group of thousands has a few nutjobs no matter how you qualify them. It's not above the baseline nutjob factor.