Firstly, let's encourage an honest discussion by calling the law with a more honest name. It should be called "Intellectual Monopoly" laws and not "Intellectual Property". Everybody agrees that we should have rights to tangible property, so calling the law a "property right" precludes the outcome of the discussion!

It is like when political factions call themselves "pro-life". Who would say he is not in favor of "life"? Everybody is in favor of "life" but that doesn't mean you agree with the political faction. Similarly, everybody is in favor of property rights, but copyright is something different.

The question is if a monopoly of intellectual products (art works, inventions, etc) is beneficial to society as a whole by striking the right balance between encouraging the intellectual production and publication from one side and allowing the society to benefit from it.

I don't have a final answer, but here is one of the very few honest fact-based analysis of the question (posed it the right way):

http://www.dklevine.com/general/intellectual/against.htm

The Copyright isn´t the only way to manage the Intellectual Property. It is the Copyleft and example of it the Creative Commons licenses. More information:
Copyleft: http://translate.google.es/translate?u=http%3A%2F%2Fcopyleftlicencias.blogspot.com%2F&sl=es&tl=en&hl=es&ie=UTF-8
Creative Commons: www.creativecommons.org