The problem with laws that allow for "I'll know it when I see it" is that - The need to be vague/broad enough to allow anything that could be <thing> to be classified as <thing> under the law - The government actors are well know for acting in bad faith, ruining the lives of people that did nothing wrong because the law allowed for it.

A teenage couple tried as adults for child pornography because they sent each other naked pictures of themselves. That is clearly not what the law intended, but the state went after them for it anyways.

Vague/overly-broad laws can be abused. Any law that can be abused will be abused.