Slippery slope arguments and things like it are not going to convince people, "just parent your kids" is not going to convince people. Not because they're wrong, but because on balance they feel like the damage to children being exposed to this content is worse than the potential civil liberty issues.
It will be very difficult to explain to people why this is not the same as alcohol being age-gated and you having to prove your identity to access it. Technically there should be no real reason we cannot do age attestation without fully revealing our identities anyway, there will need to be trust at some point in the system but the reality of the real world is that there is already and it's far less secure than we'd like.