As a reader of /r/nofap subreddit, I have learned that porn have had a very negative impact on a lot of people, and it is certainly not healthy for very young people (or even kids) to have easy access to it (as the situation is now).
I am just not sure if I would support other categories to block (like "esoteric material"), but regarding porn - good idea. You can opt-in if you want, can't you? The only problem is that if there are more adults in a household, and only some of them wants to opt-in.