The Emperor Protects

It is really not all that hard to get away with murder. A basic amount of foresight and prep will get rid of enough evidence that the police either won't find the killer or will be unable to make the charge stick.

Despite this, most murders do get solved, because someone who decides that murder is the solution to their problems is probably not the kind of person to be levelheaded and careful enough to avoid getting caught.

I think something very similar is true of sockpuppet accounts. It's not that hard to make a convincing sockpuppet. However, people almost always make sockpuppets as a way of defending their egos, of making it look like they have more support than they actually do. And this passionate defense of someone the sockpuppet ostensibly doesn't know and has no reason to care about is a dead giveaway. So if you want to validate a sockpuppet you have to lose an argument to it. You have to get owned. Once it makes you look like an idiot, basically no one will ever suspect it again.