You just said that DMCA is separate from copyright and thus fair use doesn't apply to it conceptually. So DMCA is not related to right to establish exclusive rights to works and etc. And it restricts the free speech. So why is it not unconstitutional? (See https://www.techdirt.com/articles/20100402/1856128861.shtml

Or another example of restricting free speech: https://en.wikipedia.org/wiki/AACS_encryption_key_controvers... ).