Many times people might put down something one or more people say or think, because they want to fit in. However DnD is not different than any other hobby. How many men are so obsessed with sports that they deny their family? Meaning, I think DnD is just another way for certain peoples to blow off steam or enjoy themselves. Same as being a football fan or baseball fan, what have you.
The difference though is sports and stuff are seen as being part of manhood or manly but when you sit around a table or computer using your brains and immagination while rolling some dice you're considered a nerd, geek,
So who is the idiot here? The one who chastises "nerds" for using their brain (when the system is so simple). Or the ones who mindlessly carry on chanting and hollering for their team to move a ball about a field.
I think the madness begins when you have so many people cheering for one thing. You draw all sorts of people and they get it started that everyone else is weird. Truth be told I think most people could care less about if you play DnD or not. However the media and a few pockets have stuck on this.
I don't think it is any less manly to play DnD. I know of many Americans who are very well built and know ninja type stuff in real life. They could smash the heck out of anyone, but they play DnD all the same. They even go so far as to promote this and are proud of it.
I think people use DnD as a way to segregate themselves and try to say you are that kind of person and I am this kind of person. When it is not really that case.
People will look at you weird no matter what you do. What might be weird for one person isn't going to be for the next. Still Role-playing Games have a level of taboo all on its own simply because people lack so much imagination.