"you can just give up all your property and go live in the forest."
And these people are wrong since the laws will still be applied there. If you don't own the land you are likely trespassing, squating, etc.
If you don't sign a contract you are not bound by it, and you are not protected by it. If the law doesn't apply to you, that cuts both ways: people can kidnap or murder you with impunity for any valid-sounding or completely-made-up reason.
Consent has nothing to do with signing, look at TOS. Same things with laws - you're subject to them just because you're in their domain.
If you agree to the law, then saying the people tasked with enforcing the law can affect you because you agreed to it is an argument that has some merit.
If you didn't agree to the law, then the people tasked with enforcing the law can affect you for a different reason: because they can. The natural state of things is basically that people can just hurt each other because they want to, and who's going to stop them? And "anyone" includes the police, and "any reason" includes "because their boss told them to enforce the law on you regardless of some-platonic-version-of-you is some-platonic-version-of-bound by the some-platonic-version-of-law"