How is that extortion, exactly? They are merely refusing to trade their labor for the price offered. This is just basic negotiation, a fundamental mechanism of any free market.

The only reason to be offended by it specifically when people do it collectively rather than individually is because in the former case they actually have enough bargaining power vs their employer to get a better price for their labor. That is, because the market is "too free" to produce the desired (low) price of labor.

And then they lobby the politicians to make it illegal to fire all of them for banding together. Extortion.

You know, if companies agree to never sell something under a certain price point it is called a cartel and it is illegal. But when workers do the same thing it's legal. Where's the fairness in that?

The fairness is in the fact that the balance is tilted so immensely in favor of capital in the first place, that workers need to band together just to make things somewhat closer to equal when it comes to bargaining power.

Of course, in the ideal world, all companies would be worker-owned co-ops, and then unions would be unnecessary.