it's always opt-in until it isn't

it is opt in until they manage to convince some government to allow them to be the contracted provider of "humanness verification" that is then made a prerequisite to access services.

Comcast is also opt-in. Except, in many areas there are no real alternatives.

I doubt Worldcoin will actually manage to corner the market. But the point is, if it did, bad things would happen. Though, that’s probably true of most products.