This site itself is, funnily enough, a good example of this (and, to be fair, an outlier). When you sign up to an account here, you're not asked to agree to any terms. There's nothing that forces you to agree to any terms of service. The site does have them[0], but you can only access them by clicking the "Legal" link in the footer, and you're never required to do so. Yet people here are, by and large, behaving themselves, largely due to good moderation on the part of dang and others.
But if there were to be a lawsuit, for whatever reason, it's potentially possible that someone could successfully argue that they never had to agree to any terms. It's a technicality, of course - again, very few people read terms of service, and if they did, you'd think somebody would have noticed this omission by now - but an arguably legally actionable one.
Which leads me back to my point - the only reason that businesses make you agree to terms of service is because if they didn't, they could get lawsuits that might be found in favour of the plaintiff. Businesses don't want that, so they include the checkbox.
Already the case.
Every single terms and conditions document is just legal boilerplate that boils down to "we can do whatever we want, while you can do nothing we don't want".
It already works like that.
> customers never bother to submit their own T&C's so they're not fairly represented
You can't. Not a question of bother.
> if you don't, then don't use the service
The problem is that this is mostly not an option. The service doesn't have competition or competitors don't have better T&C. Sometimes, like in the original commenter's example, there is a legally enforced monopoly.
At least the government has to enforce certain rights when using government provided services.