The counter-counter-argument is that such a shift will not occur while that harm is being delayed, which leads us on to…
- Accelerationism.
I agree with what you said, up until this point. Non-electoral strategies are not harmed by voting because of accelerationist reasons, but because the messaging becomes muddled.
We have these two horrible, awful parties no one really likes, politics is increasingly driven by "negative partisanship," just a question of which party you hate more, and then everyone on the other side is assumed to be fully on board with the worst aspects of their side, when in reality almost everyone is following this same "lesser evil" logic, and it's really just a question of which party's faults they're more aware and conscious of. One of the biggest advantages to non-electoral strategies is that you have the opportunity to distance yourself from that and define what you actually stand for and don't stand for yourself. Someone who (correctly) sees someone like Joe Biden as a slimeball, could be more receptive to leftist ideas if they're decoupled from him.
Now, you take a protest, a union, whatever, and it takes an official stance endorsing a politician, now you're gonna be defined by that politicians words and actions, and unless it's someone you can really trust and stand by, you're right back to square one.
Point is, accelerationism is stupid and doesn't work, and I can't say that no one believes it, but I certainly don't (although people often assume that it's what I believe despite everything I say to the contrary). We can look at history and see very long periods of time when things were horrible for a lot of people and they weren't able to change things just by really really wanting them to, because they lacked power and organization. It can also just lead to the left straight up getting exterminated, as has happened many times in history, like Nazi Germany, or Iran under the Shah, or the mass killings in Indonesia under Suharto. Sometimes, the bad guys just win.
Imo, anyone who actually believes in accelerationism is a fool who doesn't read theory or study history, but it mostly just exists as an insult or accusation, rather than being something people actually believe.