I don't see how playing a lot of video games prevents being a functional adult.

It's no worse than reading a lot of books or watching a lot of TV shows, activities that are not disparaged as much.

I guess it comes down to time allocation. If you're spending "a lot" of time on it but not so much that it precludes conducting the rest of your life in a functional manner then why would spending the same amount of time on porn (or any other supposedly degenerate activity) be any different?