Not all things need consent. You don't need the consent of someone violating other people's rights to punish them. You don't need the consent of 100% of the citizenry to make a decision on how to expend public funds. You do need someone's consent to take private income from them. Income taxation is wrong for that reason.
If the argument against a mostly functional existing government is that "not everyone consented unanimously and willingly", I think the claim that to require such makes things less functional is an in-bounds claim. You can argue that I'm wrong, but you will have a hard time convincing me that my claim was non-responsive.