My personal view is that, unless your are actually cheating, no method of winning is actually cheap. I have a friend that thinks using the Gamecube C-Stick to do smash attacks in Melee and Brawl is "cheap," which I disagree with. Besides, doing things like only spamming one attack is usually only useful against players a lot less experienced than you. Trying that against a Smash Bros tournament master would just get your butt kicked.
The only thing I'm not sure about is certain techniques like snaking and wave-dashing, which may or may not be glitches - not advanced techniques intended by the actual developers. Regardless, I don't play against people that use them, so it doesn't matter to me whether other players take advantage of them. However, I'm not fond of people who claim that Brawl and Mario Kart Wii were ruined just because they took those things out. Complain about the lack of new content, complain about the items - I don't care about that, but saying that you won't even play those games just because you can't dominate with a questionable technique isn't my cup of tea.