We shouldn't be discussing how to most effectively infringe upon people's personal liberties before first discussing whether there's one iota of evidence that these liberties are to blame for extremely serious issues you mentioned. The root cause of these problems is almost certainly a lot closer to the general state of economic and social hardship than porn.

Of course it's a lot easier for those in power to divert attention to a moral panic like porn instead of acknowledging that our economic system and core values are making people depressed and hopeless to the point that they're becoming incapable of performing the one thing they've been optimizing for over millions of years of evolution - reproducing.