VPN, Tor (and similar, like I2P), every imaginable P2P network, proxies, all non-http protocols (smtp, ftp, nntp, xmpp and other instant messengers and so on) can all transfer any kind of data, porn included. And a ton of other things. Heck, I'm quite sure there's a minecraft mod where you can assemble JPG-images out of the blocks and view them that way. And then you can use stuff like uuencode where you can use anything that can move plain text to transfer binary data.

There's no way to block all of that unless you shut the whole internet down. And even then you can still trade good old playboy-magazines with your friends. VPN in itself has very little to do with the actual problem, beyond that someone apparently noticed that their current "save-the-children" iteration had pretty large holes in it.

You can't block VPNs without blocking the entire internet. You can block known VPN services, but you can't prevent people from hosting their own.

Some known VPN protocols could be blocked, using introspection tools. However, this would just render corporate VPNs useless. VPN traffic is just bytes, and so is WebSockets. Good luck figuring out whether my HTTPS traffic is legitimate internet traffic, or masked VPN traffic.

Depends on the VPN

You can't block porn completely without blocking VPNs. If you connect to a VPN that's all they can see.

This makes it sound like VPNs can ONLY access porn. lol