There's a constant tension in climbing, and really all exploration, between pushing yourself into the unknown but trying not to push too far. The best any of us can do is to tread that line carefully.
To be clear, I normally climb with a rope and partner. Free-soloing makes up only a small percentage of my total climbing. But when I do solo, I manage the risk through careful preparation. I don't solo anything unless I'm sure I can do it.
'Dirtbag' is just the term we use, like a 'gnarly dude' in surfing. Within the climbing culture, it means being a committed lifer: someone who has embraced a minimalist ethic in order to rock climb. It basically means you're a homeless person by choice.
I have a journal of everything I've ever climbed since 2005. For the entry about free soloing Half Dome, I put a frowny face and added some little notes about what I should have done better, and then underlined it. Turns out that is one of my biggest climbing achievements.
The diet for climbing all the time isn't really different from the diet for living. It's not like cardio sports where you're burning a bajillion calories every day.
I think it's great that so many people are enjoying climbing. I've always loved climbing; I don't see why other people wouldn't enjoy it just as much. As long as everyone does their best to respect the areas in which they're climbing, I don't see how the growth of the sport could be a bad thing.
Climbing is definitely very much strength-to-weight ratio. At the same time, I've never dieted or restricted calories. You're just sort of mindful about not getting plump.