I don't think this is the topic for a debate on parenting philosophies or deciding who is/isn't a good parent per se. I like the original topic and where it was headed before we dove into "Honor thy father" versus "Do as thou wilt" or however you want to describe these divergent notions. I hope the children of all the parents on this board and in general grow up to be happy, healthy, and well-adjusted and do you guys proud, but knocking each other over the heads probably won't measurably contribute to that end.
No, I don't have any kids. I'm 25. The closest thing I currently have to that responsibility is a cat on par with a small toddler. I would totally let her play D&D if she'd stop trying to lay on top of my open DMG when I'm using it. I also played a lot of pretend with young children when I worked briefly in child care, and I firmly believe that D&D is pretend with all of the playground rules now "codified" into numbers. I find putting D&D in those terms to help at least allay some of the suspicions of those who think I am learning black magic and will find my soul being dragged into hell.
I do not think it's useful to that type of person to say "But it's 4th edition!" Doubtless they don't actually know that there have been different editions or that there's any significant different in terms of play between them, because in terms of "substance"--that is, a fantasy game with magic, demons, gods, etc., the game hasn't really changed (despite how individual game worlds are developed, polytheism, demonology, dualism, etc. are presented in the source texts, and there are faithful people who object to that stuff on principle whether or not you can use the information in the books to actually summon demons or force angels to do your bidding). To them, I say don't play--but don't get in my way, either. However, in the eyes of the law (if not necessarily of my distant, beloved parents), I am an adult, and I can do what I want as long as it's not illegal, so I get to do that. Short of violating my personal rights or scheduling courses during game nights, no one can stop me, either.
Both of my parents played D&D, and my father got me into it. My grandmother always asks us if we "won" after game night (sadly, I haven't been able to play with my dad's group in about a year--being a few states apart does that). My maternal grandmother probably wouldn't have been so relaxed on the topic; the indicators don't point to it. Now, however, I'm an adult, and she's not really worried about anything I watch influencing my behavior towards irresponsibility or violence. She never really minded me playing videogames, but Rugrats really bothered her when I was a kid watching Saturday morning cartoons.
Internal inconsistencies are part of what being human is about. Someone's parent may have no problem with their kid watching Law & Order: Special Victims' Unit but really flip out when the same kid wants to watch a cartoon with stylized violence, let alone play a game where the kid simulates said violence (even without the sexual content of SVU).