Everyone who is big is not on drugs. Anyone giving you that picture of bodybuilding is doing everyone a disservice. Chances are, the PRO'S, as in the guys who walk across the Olympia stage, are on shit. There are many big guys walking around who aren't.
As far as your last question, I don't think you have a clue how much effort, training and consistency it takes to put on a great deal of size. It takes a conscious effort to get that much bigger. It doesn't happen by accident and most of the people with any truly credible size on them have been training for over 10 years. That means your last question is the wrong question to ask. Why? Because no one ever got humungous by mistake. If you don't want to get bigger, you stop eating more and stop lifting more. I have never run into the person who said, "I never wanted to be this big, I just woke up one day big as a mutherfucker".