Honestly, you need to remember what is happening when you brew. You're essentially creating a big batch of food for some foreign organism to eat. In science we call it a substrate (same with mycology). And usually you have enough yeast that it will take on its own, and it will quickly overcome any invaders.
However, some times the invaders outnumber the yeast, and when that happens you'll get vinegar.
Still other times you'll get invaders and they'll ultimately get overtaken by yeast, but not before byproducts of their eating sugar get put into the brew. Now I know this usually doesn't happen with brewing, but when growing mushrooms it can be deadly (chemicals produced by, say, black mold can be transferred by the good mushrooms and become dangerous to eat).
So, I'll stick with sanitation. This is one time I trust the science.
However, some times the invaders outnumber the yeast, and when that happens you'll get vinegar.
Still other times you'll get invaders and they'll ultimately get overtaken by yeast, but not before byproducts of their eating sugar get put into the brew. Now I know this usually doesn't happen with brewing, but when growing mushrooms it can be deadly (chemicals produced by, say, black mold can be transferred by the good mushrooms and become dangerous to eat).
So, I'll stick with sanitation. This is one time I trust the science.