It's illegal because there's a law against it; IP is not a legal term, it's a term for constructing laws, and persuading people they're good laws.

It's easy to lump all IP issues together, as indeed many people on both sides do; it's not really very helpful, though, when current law is very different for patents, copyrights, trademarks, and trade secrets.

While I am generally rather away from the IP side of things (WRT patents and copyrights, at least), it's crucial to make clear arguments on each issue, or you won't be as persuasive as you could be. It's clear you understand both the distinctions I mentioned above, but it seems you're not separating them in your argument effectively; as I'm an ally (though not a friend) in this fight, I wish you'd do better.

My arguments:

Patents are wrong, because an arbitrary restriction placed on me by the government forbidding me to make and sell something is an infringement of my property rights; I am not harming anyone else's property, and the only valid government intervention is to prevent infringement on another's property. (For the purpose patents serve, namely to allow the inventor a profit, trade secrets work out nicely; inventors can shift to those for protection, so I'm not advocating such a radical shakeup as it might at first appear, but this really doesn't matter...)

Copyright is even more clearly wrong, because it prevents the exercise of my own rights with pen and ink, without so much as involving a transaction with another person; it's transparently clear that I cannot be harming another's property, yet the government seeks to impose a restriction on it. (Again, for things worth protecting, protection is available; you can require people to sign a NDA before you give them your book, and then that is binding, preventing copying contrary to the terms of the NDA.)

I don't think economic and social damage have a thing to do with the laws that should be made; it's all about property rights and voluntary contracts. Moreover, what activity of theirs should be made illegal? Filing for the application of government force in their favor that is provided for by law? If you just shut (for example) the USPTO down, I don't think making the sending of patent filings to their old address a crime is necessary or useful... (This last paragraph, of course, is the place where I differ, making us mere allies...)

Cue replies stating that your post had them persuaded, but they ran away screaming when they saw mine...