When nobody's done something before, there are lots of unanswered questions.

Is it even possible? Will businesses my voters like and use a lot just leave my country entirely? Will companies be able to develop privacy-preserving age check infrastructure? Will the press present it as a 'Chinese-style Great Firewall' or be more supportive of it? Will the blocks all be trivial to bypass? Will the large number of porn users in my country form a cohesive voting block? Will a powerful pro-privacy, pro-free-speech lobby emerge to challenge this? And will they be backed by powerful, well-funded US interests like Facebook and Google?

Australia simply showed the world passing this sort of legislation isn't political suicide.