It isn't so much a problem with democracy as it is with human beings. I think of democracy as averaging out things so the swings related to specific types of evil, shortsightedness, good, bad, aren't as big.

More authoritarian systems have higher variance, even if specific instances might be "better". I use scare quotes around "better" because I would argue giving people democratic power is valuable even if they do dumb shit with it, so you can't just compare democracy to authoritarianism. The latter simply lacks one key thing that democracy gives: some self determination.

This is not a defense of any particular contemporary realization of democracy.