Various opinions and layered discussion but I will keep it simple. Bad movies have their own magic and could be argued as it's own sub genre in current society. That being said bad movies that fail in every level (acting, effects, cinematography, writing and so on) makes me appreciate the efforts on good movies.
This to be fair. Most people tend not to notice good stuff when it's done right. But it really noticable when it's done wrong. You won't be able to truly appretiate great writing/camera work till you are exposed to some of the bad stuff.
Also bad movies(especially ones taking itself seriously while failing on every level) are a whole lot of great fun :D