I don't really get this argument. You lose 100% of income, assuming this is your only job, but only until you get another one, which could be right away, and in the meantime if they terminate you without cause you get unemployment for long enough that most people will be able to find another job.

Meanwhile this criticism is inversely correlated with the utility of a union. If you're in a market where the company is hiring unskilled fungible peons, and you try to unionize, they can just let the union walk out and hire a bunch of different unskilled fungible peons. So it doesn't work for e.g. Amazon warehouse workers.

For a strike to mean anything, the company has to have high turnover costs in replacing employees or a scarcity of skilled labor. But then that's true of the individual employees as well. So then it isn't needed for e.g. programmers to be able to negotiate beneficial working conditions, and you're paying the overhead for what you could get without it.

What does that leave for where the union is doing something good?