The problem with letting things fester is that they tend to grow and get worse while they're out of sight/out of mind, until they eventually burst out and spread toxicity everywhere.
One of the benefits of free speech is that the nasty stuff gets exposed. When it's exposed then you at least know where it is. The only problem is if the nasty stuff doesn't get labeled as such so it can be dealt with, and instead is treated as if it were normal and allowed to continue spreading (e.g. police turning a blind eye to far-right gun nuts intimidating voters).