I practice/teach martial arts 2-4 times a week. People pay me to hit them, and that's why it's so cool :-) Joking aside, it's a great way to stay in shape, and the people at my dojo are fantastic - they're like a second family to me.
Could you elaborate on what kind of MAs are you into? I always wanted to try, but I hate the hyper aggressive, macho-alpha-thing attitude that I suspect I'd find in, say, the box gym down the road. Is it even a true stereotype?
As for your stereotype, it really depends on the gym. I'd say if you're looking to do mixed martial arts of boxing, the probability of finding a meathead-alpha-gym will be higher, but there are MMA and boxing gyms that are also laid back. So in a nutshell, you really have to take it on a gym-by-gym basis. If you're looking at getting into MA, find a place close to you, and sit in and observe a few classes before giving it a try, and be aware of the vibes you get from it. If you get a decent feeling about the place, see if you can try a lesson or two for free, to see if it's for you. Repeat this process for other gyms and soon you'll find the one for you :-)