I think instead of parents constantly telling kids not to watch and only watch certain movies is far less liberating than when movies are just rated for viewer's discretion and kids have freedom to watch what they wish and be happy for it. I think it is much for fair for the adult knowing that the content they watch is appropriate enough and the kid who gets to watch the movie that was desired.
In my opinion, movies should be rated and ratings should be strictly enforced in public. Children should not be allowed to view movies showing private adult content or graphic violence on their own whim or pleasure. Parents can monitor what the child watches at home but at the theater ratings and rating enforcement should be upheld.
Movie ratings were always meant as a guideline, anyway. Parents are expected to be the final word on whether or not a film is acceptable for their children to watch, and there are dozens of guides on the Internet available to help them make that decision. Ratings should not be abolished.
Personally, I've been affected by this. Being under the age of 17, I'm not allowed to watch an R-rated film by myself in the theater, even if my parents are OK with it (which they usually are, I mean they let me watch Goodfellas and Apocalypse Now). Ratings should exist, but not actually be like enforced, just a guideline.