Indeed, I'd list the MRA/PUA/GamerGaters as a much greater risk to young males (directly; young females as a consequence). I'd probably have the alt-right/conspiracy loons above porn as well.
[Citation needed.]
Have a look at Google Scholar for a plethora of papers about cyber-bullying, grooming, self-esteem issues (mental and physical), pro-anorexia blogs, etcetera. You can combine the keywords "internet" and "children" with any of the above to get an extensive list of papers on each topic.
I've never seen a peer-reviewed meta-study that suggests that the Internet is any more dangerous for kids than ordinary life.
EX: Cyber-bullying has many positive outcomes preparing sheltered children to the kind of people that live in the real world. Just look at what happened to the US hikers captured by Iran for an idea of what a sheltered upbringing results in.
That's what this is all about isn't it? There is lots of stuff on the internet that may hurt a child's development, and I honestly doubt porn is one of the bigger bad influences. Kids are growing up watching popular peers give them beauty and fashion tips or perform dangerous stunts and pranks on extremely popular Youtube channels. Of course all you see is the side they want you to see: the successful prank with hilarious consequences, the perfect look by that pretty girl with the perfect figure.
But left to their own devices your children won't see that girl's bad hair day, or the stunt that backfired and landed one of the kids in hospital. Your kids won't realize that the brand of lipstick the popular beauty vlogger promotes also sends her plenty of free samples in return for the favour, or that that hilarious prank was staged.
It's our responsibility as parents and educators — as adults — to teach kids about this.
Now for porn this always gets tricky, because a lot of people would like to stick to just the basic birds and bees (if even that) and just pretend that sexuality is something you receive with your drivers licence. It doesn't work that way, and believing that blocking a vaunted digital commodity will make it go away is an age-old fallacy. There will always be that one kid who can get the goods, with that one app or website that completely circumvents the blockade.
Meanwhile you get to register for your approved pervert ID if you actually want to comply with the system and watch porn. It boggles my mind how anyone can think that this will benefit society rather than take another step towards a full Orwellian surveillance state.
> I'm all for a better solution, but nobody seems to be proposing one.
You are probably doing all right already. The computer and tablets stay in the living room where you can supervise incidentally until they reach the teenage years. And then the smartphones stay with you after bedtime. For the rest, it is up to you to set a good example, and to explain the world to your kids as they encounter it. That means talking about sex too, and that means explaining what they are looking at when they do stumble upon adult content — not acting embarrassed and making them feel guilty as if they've bitten into some forbidden fruit.
"Oh this is just adult sex, you'll understand better when you are older. Any questions?"
If it really bothers you; install filtering software. Filtering the parts of reality deemed not yet suitable from your children is responsible (just don't pretend it doesn't exist); filtering it from society at large is unbearably sanctimonious.