You can always get another job, and being good at what you do should increase the probability of getting a new one.

Everyone knows about business cycles. It's worth saving for the unexpected layoffs so that you can make it through. To reiterate, knowing I could not have a job tomorrow every single day is not enough justification for giving up my ability to self represent. Plus, I don't have to pay people for the privlidge of losing my independence.

You can probably get another job yeah. Can you get another job with the same total comp and benefits? A lot of people are finding that that's not the case, you might preserve your salary but give up stock options and remote work, etc. Also, it's just a pain in the ass.

I think this reasoning is pretty labored. Sure there's some small percentage of engineers who are eminently employable and don't care to unionize. It benefits everyone else though, and even those "elite" engineers benefit from unionization, as unions have to represent everyone. I feel like there are tinges of, "I don't want to pay union dues if I'm not in the union" or "everyone thinks they'll be rich someday / are an elite engineer so they don't want to tax the wealthy / unionize", but idk, these are old, bad arguments.