Should I steer my brother away from taekwondo?

Well it's not like that at all. And good teachers teach you to avoid a fight by keeping distances and only as a last resort use what you've learnt. It honestly does work in self defense, some people say it's bad because they think their style is best and all the others stink, which isn't true. It's a martial arts, so it does teach self defense. Also if it's something he wants to do, then let him, there's no point getting him into a style he's not interested in.