Haven't heard of T+ before, some new rating for 21+ or something? Or does it stand for teen+?
I think parents need to control their children if they really expect to see a change in attitudes towards rating games/videos/movies. If their child is someone who gets what they want all the time (spoilt) and never has to face any kind of consequences, then allowing them to delve into any video game or movie/show will often have negative impacts on their character. But mum and dad will sit there thinking "oh he's fine, he's not really like that" when the kid is tearing up some people on assassin's creed or something, then ignorance will be the downfall of the family when the child decides he can do anything he wants and puts risk before himself or another person.
Another example, if your kid decides he wants to sit with a magnifying glass on an ant hill and watch it burn, then you may need to prevent him from being exposed to violent games. Violence breeds violence, or in this case, ignorance breeds violence.
Tldr: Control your children, don't let them get away with life without facing the reality of consequences. If you feel that your child is mature enough to accept the boundaries between the real world and that of a video game or movie, then by all means allow them to enjoy whatever they want