premise: It's certainly the case that we are asserting, in light of the changed circumstances, that the opportunity to build upon works within the public domain is a fundamental First Amendment interest, and that the First Amendment values, vital speech interest at stake of this case, is that the public domain be permitted as a source for cultivating work about our culture without unnecessary legal restriction.
hypothesis: public domain should not have cumbersome restrictions
reason: Public domain should not have cumbersome restrictions refers to legal restrictions which, in context, states that there should not be any interference from when adding to public domain.