We have lots of evidence of chilling effects from copyright law.

I suspect that many of the people who are creating things which violate copyright law are simply unaware that what they are doing is against the law (they feel that they have rights which they actually don't) or they misunderstand the law (See: "No Copyright Intended" descriptions on youtube videos).

Some certainly also think that enforcement is lax enough that they won't be caught, or at least not before others have mirrored the content, or that they won't face meaningful consequences when they are caught, but I think we absolutely cannot say that the existence of copyright violations proves that the laws aren't hurting us by preventing popular original works from being made.

> The only thing they're prevented from doing is using someone else's IP.

Consider what happened with blurred lines (see https://mcpherson-llp.com/articles/crushing-creativity-the-b...) We know copyright law hurts people that aren't using anyone else's IP.

This guy has a lot to say on the problems with the idea that using other people's IP is a bad thing in the first place:

https://www.ted.com/talks/lawrence_lessig_laws_that_choke_cr...