Its not that I wouldn't consider exploiting a patent if had one, but in general patents do not necessarily benefit society. Here are some reasons why, bits and pieces culled from http://fare.tunes.org/articles/patents.html
, which say it better than I could:
Indenture of Employees
Consider the consequences on employees, including inventors among them: Employees who develop proficiencies the application of which depend on patents find themselves suddenly undervalued in the labour market. Indeed, patents reduce the number of potential employers, since only license holders may take advantage of these proficiencies. This indenture of employees to privilege holders means reduced mobility for employees in general, and thus a more expensive and less efficient job market. In the end, the companies themselves will have to pay higher wages for less adapted employees. Everyone loses with patents.
Contradiction between Patents and Public Research
Patents were meant as an indirect way to foster innovation; so it would be economically absurd to patent the results of public (tax funded) research: indeed, in the case of public research, the public has already paid for the research, through taxes, so it needn't pay for it a second time; the only result of the patent is the monopoly, that restricts the use of the technique that was paid for, and deprives the public from both the technique. More competitors, as prohibited by the monopoly, could only mean more deployment of the technique. The patent is absolutely no incremental encouragement to innovate for public research, since the encouragement was already completely given as public funds; but the patent will still have its detrimental effects on the public, and its limiting effects on the use of the discovered technique.
Loss of Liberty to Customers
With industrial protectionism, innovation is no longer consumer-driven, but producer-driven. The evolution of any product line resides on the shoulders of a one monopolistic provider. A consumer cannot compare between providers and choose one that suits him better. Thus, the risks for the customers are high that, even in good faith, the monopolistic producer will lead the whole industry into quite suboptimal (or sometimes catastrophic) choices. The overall result, for customers, is thus not only bad quality of services and high prices, but less liberty in choice of technological solutions, and thus solutions that are less adapted to their needs.
Delays in Publication
Patents were allegedly made to foster publication of inventions that would otherwise remain secret. But actually, patents result in scientific findings being published later, and in disuse of techniques that could not in any way remain secret. Indeed, due to patent regulations, research centers will hesitate to publish results in ways that would prevent their patenting them. This is due to regulations that prevent patenting of previously published material. In such case, the patent system will actually delay (or even suppress) publication of material that would otherwise be published.
Technical Lock-in and Research Avoidance
Once a patented technique is successfully spread, it creates incentives for a whole range of nasty behavior from the privilege holder, whereas other people are forced into passiveness, or strongly incited into it. Successful patent monopolists, deriving lots of (socially destructive) revenues from their patents (which is the primary economic effect of protection), are incited into finding ways to secure these revenues. The monopolist will try to accumulate new patents regularly, so that even when his original patent expires, he still has a monopoly on the modern form of the technique. At first glance, it looks like this will foster innovation, but then, the kind of innovation that is incited is not superior ways to use the technique, for the benefit of the public; it is ways to secure monopolistic revenues. This means that a large part of the research will be diverted from making things cheaper, simpler and better, into making them more expensive, more complex to interface to; Companies that hold patents will tend to fund research that depends on their existing patents, and to discard research that circumvents their patents.