On the extremists among Bernie's supporters: as has been pointed out by myself and now numberthirty Bernie is never going to be President. So whatever feelings they had or behavior they engaged in (or whatever behavior their opponents engaged in), or whatever grudges you might be holding onto from the '16 or '20 Primaries it's not worth holding onto. Extremists are going to be extremists, and they're going to remain on the fringe. Memes are not going to change that.
On "taking away their tools", I don't feel like its mine or anyone's place to censor free speech unless and until it rises to inciting violence or other common sense restrictions we've all pretty much come to agree upon. I understand why private social media companies tend to be more heavy-handed in these situations (looking to avoid lawsuits and accountability), but they're not going to do that for a Bernie meme where he's doing whatever while sitting in mittens. Nor should they, whatever "slippery slope" you might believe it leads to. I also don't believe I (or anyone else reading this) could determine what lies in the heart of those creating all of these memes, so who exactly do you suggest we target for meme-banning? Anyone who voted for a non-centrist candidate?
On the name not sticking, again Obama won and history is written by winners. Like Kamala Harris "believing Tara Reade's account" when it was politically convenient then jumping on board for the number two spot, Hillary tried to slime Obama's followers but then campaigned hard for him when it was clear it was over for her. Had Bernie somehow pulled off an upset she would have done the same for him. Doesn't mean there weren't bad actors in the Obama campaign (or Clinton campaign, or fill-in-the-blank campaigns). It's politics. People have strong feelings and play hard. If anything a valid criticism of Bernie and his campaign was they didn't play hard enough.
On the election being a blowout and Biden flipping red states, I'd again argue it was less about excitement for Biden (I like the guy, but let's be honest) and more about excitement at the prospect of voting Trump out of office. Saying Biden's bland and middle-of-the-road and not very exciting is only a knock if you buy into popularity being an important part of being a competent President. As stated before, I don't think it is (beyond getting people to let you do the job). I can't prove that I'm correct that it was more about Trump than Biden, and I'm sure people much more intelligent and knowledgeable about these matters are going to have differing opinions. Guess we'll just have to agree to disagree here.
On the narrative that Trump was easy to defeat, my answer is he should have been in '16. He had no qualifications, he turned off Evangelicals and fiscal conservatives who literally had no idea how or if he'd govern. Most held their noses and hoped he'd give them a tax cut and maybe a Supreme Court Justice or two. It was a gamble that paid off for them. I believe if Biden had run in '16 he would have handily defeated him. Again, not because of popularity but because he wasn't weighed down by tons of baggage like Clinton and Trump were and because he's competent and (when at 100%) likeable enough.
On Bernie and "excuses", I'd say just my explanation by way of speculation. Again, agree to disagree. Every politician has weaknesses. Bernie had a few. 1. Probably shouldn't have been in the main event. 2. Was hyper focused on economic issues for the poor and middle class, and had tunnel vision. 3. Wasn't really a political player, and never really got the hang of "the Game". I'd like to point out you appear to have very strong feelings about the man and seem to feel he has no virtues, and take an almost personal offense when someone points out even obvious and widely accepted flaws in other (usually more centrist) candidates. I'd also like to point out that you seem worried about feelings winning out over facts in politics. This seems like a bit of a contradiction to me. So to help, I'd again like to point out these facts:
1. Bernie Sanders will never be President.
2. "Bernie Bros" will never again be relevant, and arguably never were.
3. A centrist candidate won and is now President of the United States.
4. You're never going to get rid of political memes, or people projecting their hopes onto potential "political saviors" It's a reality. The best you can do is try to accept that and maybe try to rationally discuss issues with them. But accept that's probably going to change their mind about as much as a meme.
When you paint a large group of people as equivalent to the worst among their number you are far more likely to have them either A. ignore you or B. actively work against you. You will never, ever, I guarantee you get them to stop and say, "Gee y'now, you're right. Those people on the fringe really do give me pause, maybe I should change my political affiliation and opinions to more closely resemble yours in your clearly superior wisdom."
It probably feels good emotionally to paint anyone who disagrees with you as ignorant or "evil" in some way. Nobody's the villain of their own story, and if you can keep your own internal narrative simple by dismissing anyone with a differing opinion as a commie/nazi/racist/radical/etc. it's probably easy to keep. But I'd guess that's also how you get people who still believe Biden wasn't lawfully elected and that any day now the military is going to pull up to the White House with vans and start loading Democrats into Gitmo. Not having to think or challenge your beliefs is far more dangerous than posting a meme about Bernie Sanders or anyone else. At least in my opinion.