1b - If it's already backdoored then there is no need for such an act, the problem is already solved.
2 - It's ineffective for it's stated goal because the stated goal is not the real goal. The goal is to enable a continued abuse of power, one which is already ongoing, and one which produces no actionable results or meaningful outcomes. Five eyes & co is upset that they're losing some of their toys.
3 - Who says governments should be able to regulate weapons? Likewise these days, who is to say they meaningfully can?
4 - Sex trafficking existed prior to encryption. The government failed to stop it then. I strongly suspect that even if the government gets it's way and breaks encryption, sex trafficking will continue exactly at the same rate. Most sex traffickers are not technology ept, nor do they need to be - the track record for capturing them is atrocious. Epstein anyone?
This is a bad faith argument. "Protecting children" and "stopping terrorists" are the siren's song of every government overreach basically since the dawn of time and yet the government remains terrible at solving either problem. I don't think encryption is really the issue preventing those things from getting resolved. I do think encryption is very inconvenient for a very snoop heavy government.