If the benefit of society as a whole is the objective then inventions are only worth protecting if they would not have occurred without such protection. An idea clearly does not fall into that category, it's worth is in the execution and not in "having it".
Back when I was actively studying this stuff, it was noted that there are four specific industries where intellectual property just doesn't work as intended. Software was one, pharma was another, and I forget the other two but a quick Google ought to surface them with more credibility than I can drop here.
That's not to say it works much better outside those industries, but it's not completely pointless.
I thought pharma relied on patents to offset the massive cost of regulatory control over the product. (FDA fees, cost of running patient trials, etc)
http://www.becker-posner-blog.com/2012/09/do-patent-and-copy...
Also, pharma companies have been known to get patents on drugs that have existed for many years- which does not support innovation (though pharma argues it supports government regulation of these drugs, which have been on the market for many years)
Dont't get me wrong, I am for abolishing all patents. Even if, say 80% of the patent were unimbigiously justified, the bureaucracy and costs it introduces are tremendous.
I would loved to know the percentage to the total budget of the legal departments of companies like MS, Google and Apple
One of the ways of making a product defensible is to patent its underlying technology.
If a software startup doesn't hold a patent, there is a chance a larger player could just copy the startup's product or service and drive the startup out of business.