The truth is... yeah, there are meet and greet rules...
Some artists don't want you to touch 'em. That's understandable, because there are indeed some creeper freaks in this word.
Some artists ban photographs and selfies, and this is understandable because you have to move people along.
Bottom line is they're people, too... so they've got quirks like you've got quirks... I think the bottom line is to be respectful and make the most out of the time you get with your favorite artists... and remember, they're people, too... so be nice.