I personally would never use stall as I don't have the patience for it, but I don't think it is a bad play style as such. People can play how they want, and while I find it really frustrating to come up against, I don't think they shouldn't be allowed to.
The only place I can't stand stall is when you only have one pokemon left and rather than finishing it off, the opponent spams healing moves without even poisoning my pokemon or anything. This way, the battle never ends as I can't KO any of the other persons pokemon and they aren't damaging mine. I hate quitting battles before they finish but I often will if that happens.