What the fuck are you talking about? Do you just want to act like you're a victim for no reason, while also acting like you have some moral highground?

Of course you can vote third party. I'd still do it strategically, but local is where they can actually win and gain influence. You can also vote in the Democrat and third party primaries (if they have them) to get candidates that suit you better.

Odds are a leftist will run under the Democrat banner, and try to win local primaries, and this is how parties change. They don't change from presidential elections (usually, Trump arguably did but I'd argue that change was happening for a long time locally first). You need to win local elections and build a power base of enthusiastic voters and experienced politicians (and donors). They usually have to prove themselves locally first, and if you aren't supporting them then you're never going to have someone you like in positions of power.

You're allowed to do whatever you want.

If you want to actually make a difference you use strategy.

The smart play is to get a Left leaning Dem nominated. Most voters aren't going to vote for a 3rd Party candidate no matter how good they are.

I'd rather vote for a mild Left candidate who has a real chance of winning than throw my vote away on my ideal candidate.