I'm gonna push back a little on that thought.

Saying "don't vote Biden" is very important, actually, and it's hardly bullshit.

First and foremost, when you are in the mindset that voting is all you can do, saying "Don't vote for Biden" opens up a great conversation about voting, democracy, racism, and pretty much any issue that is tied to the US government. These conversations are important, and must happen. There is a radical praxis to not voting, whether you'd like it or not. If voting for one of two parties is the only acceptable form of political action, than not voting, voting third party, or something else (such as setting up prefigurative structures) is a good, radical action.

Before you point this out, I do have issue with how many leftists, communists, and anarchists just skip this conversation online, or say something like "Oh, these conversations have happened before, just read this book" or some nonsense. I get that having this conversation a million times is exhausting, but it's important. You don't have to do it every time, but if you are able to jump in and take over, you should!

If this conversation is good, it should point out that the supposed "democracy" we have is not only fragile, and being taken over by fascists, but that it was really only a democracy for a small group, not the idyllic idea of the majority getting their say and representation. It should also point out that this "democracy" has been a tool used against minorities as a cudgel, bringing pain and suffering for centuries. It should point out that there are many positions that the majority of the public want, like social/single payer healthcare, yet we have a top aide to the democratic speaker of the house, telling lobbyists to not worry about it!.

Second, Biden is not entitled to any voting, and he needs to be reminded of that with the threat of non-voting, and anti-voting advocacy. The idea that someone is entitled to your vote on the basis that they are not someone (IE: the lesser evil) else is antithetical to the core concept of democracy: bringing power and representation to the people (often through majority voting). Imagine that you have two candidates in a FPTP voting system, one person that is 100% hitler, and another who is 80% hitler. It is obvious that the lesser evil is the one that is 80% hitler, but if the country consists of primarily people who want a 0% hitler candidate, how is the 80% hitler, the lesser evil candidate, a representative of the people? How does that 80% hitler candidate represent the majority of the people? Isn't that antithetical to the very concept of democracy that such a candidate can exist?

I get that it is a tactical position to vote for biden, considering that trump is so awful. I don't think it's fair to criticize someone for voting this way because it is genuinely a logical and reasonable conclusion, but I do think that the thought process that got them there needs a bit of evaluation.

Third, threatening to not vote for biden (and especially staying true to that threat) is good, actually. I've already mentioned that biden is not entitled to a vote, but it's also important to mention that biden is a human being who has the capability of acting to fix this. "Remember to vote for the lesser evil!" is, unfortunately, placing the blame for biden's actions on the individuals affected by it, rather than the person who did the actions in the first place. Thinking solely from this mindset does not hold biden accountable to his actions, and often leads to blame being placed on people for not voting against their interests.

Finally, you mention "writing to your congresspersons". I think this is a great idea, but it should not be the only mechanisms of political action aside from voting. I can safely tell you that this is often ineffective. One of my best friends was an aide to a representative in congress for a few years before and during Trump's presidency. He has been at the receiving end of a calling campaign from some bigots in my state advocating for an anti-trans bathroom bill, and he told me at some point, he stopped paying attention to it, and he was getting pissed off because it was taking up his time that could otherwise be spent working with residents of the state with other problems, such as social security, VA benefits, etc.

Since my dinner break is coming to a close, all I can really do is be that annoying leftist who shoves a book in your face and recommend a short(ish) book that I loved reading about democracy and voting, and the myths it promotes. Crimethinc.'s "From Democracy to Freedom" is freely available as a PDF online through the publisher, Crimethinc.