* Conflict with fundamental personal liberty: Mill's idea that we have unrestricted liberty except to the extent that it injures someone else, is fairly standard. But IP conflicts with that, yet IP is not fundamental, not grounded in physical fact. (See Koepsell: http://www.hxa.name/articles/content/ethical-case-against-ip...)
* Cannot be justified on the basis of harm: One could justify rights by showing that lack of them causes harm to those denied. But IP represents no physical relation where any harm could be rendered. (See Wilson: http://www.ucl.ac.uk/~rehbjgs/docs/could-there-be-a-right.pd...)
* Does not make complete sense as a generalised rule: The idea that a moral rule is generalisable, as a critical feature, is also standard (probably more so). But if everyone owned IP equally much there is no advantage, and everyone would be better off freely sharing copies. (And indeed, what do we seem to see amongst similarly large corporations? They buy big patent portfolios and agree, or tacitly accept, truces between them.)