Why not?
The greater the power imbalance, the less free the choice. Social networks are a great example of this. You can choose not to use a particular one, but what's the alternative if everyone is already on that platform? You can go without, but what if it's LinkedIn, and there can be a real impact on your career?
But you do have a choice. Don't use the site if you don't consent to its rules. Pretty straightforward choice.
It is, if you don't think the rest of what I wrote is worth any consideration.
Nobody is suggesting companies provide free services. We're saying that personal data is more than commodity, and we should be looking to more ethical business models. And we won't be sad to lose companies that can't adapt.
edit: And I don't think my point was silly, but I'm also not really libertarian. So I don't think it's acceptable for companies to abuse their dominant position to make things worse for society at large.
From what I've read, opt-in is only supposed to be used when there's an actual voluntary choice, and "allow us to share your data with 3rd party trackers or we block you" doesn't count as a real choice.
It should be treated in the same way as opting into marketing emails. Totally optional. Not opting in shouldn't totally break a site.