You know that even in capitalism there are laws protecting against what you are advocating here? From public education to stock market to whatever. Again the right to commercial use and the right to knowledge or information should have nothing to do with each other.
I'm an IP attorney, actually. Specifically, Entertainment Law (which primarily deals with Copyright, but has some Trademark issues as well). I also have a degree in Economics & Philosophy and an MBA in Sports & Entertainment Marketing, and will be attending a Tech law conference in Austin 2 weeks from now.
So, yeah, I'm pretty familiar with the topic.
Commercial use is one facet of the right to knowledge- the right to exploit it commercially. IP laws are one factor in creating the barriers to entry in a particular market. Those barriers matter. If the barriers are too high, nobody enters the market until the price of the good is incredibly high. If the barriers are too low, then entry is so easy that there is minimal profit to reinvest in R&D.
Even the "educational purpose" loopholes cost- you can't use so much of an IP in that manner as to render the IP valuless, and to gain more knowledge, you must pay- typically to some educational institution, be it a school or a company's internal processes...which typically comes with a contract including a "non-compete" clause (which economists would call an "opportunity cost").
The architectural monuments and the monumental art in museums you are talking about have nothing to do with copyrights.
No, those in particular are definitely within the public domain now. But in their day, they were as vigorously protected as the laws of the days allowed.
It is also practically irrelevant because noone actually wants to build an exact copy of some other monument.
You'd be surprised at how much design work (architectural and otherwise) gets copied in some way, shape or form. Seldom is the work a 1:1 replica, but the law doesn't protect against perfect duplication, it protects even against partial duplication to a certain extent. Its a fact-dependent matter for the courts to consider, not a simple % formula.