I agree that creating barriers to access in general, and harder barriers for under-18s, is a good idea. There is a lot of room between "showing porn in kindergarden" and "anti-porn inquisition" to work within.

It doesn't even need to be made illegal. Making age verification a requirement would help a lot. Actual verification, not click-thru "yes I'm 18, wink, wink". Ensuring privacy while preventing access to most minors would be the main issue any technical solution would have.