Whether good or not, conscience exists and can be used as tool or weapon

Brett, Chad and Adam make a number of good points. In particular, their posts raise some common themes I'd like to highlight and respond to:

First, is conscience unambiguously a good thing (and by implication, is selfishness always bad)? Of course not!

Selfishness can be great when it motivates people to do things that make the world a better place, whether one defines "better" in utilitarian terms or more philosphically (e.g., "flourishing"). I'm perfectly happy to let selfishness be the primary motivation for the guy who clears the snow out of my rented Ithaca driveway.

But there are times when selfishness is suboptimal; think the classic tragedy of the commons. Here, sometimes, conscience (unselfish, prosocial behavior) produces better results, because it can motivate people to do things that make the world a better place where material incentives are too expensive, too awkward to employ, or otherwise unavailable to do the job.

Second, that is not to deny that, just as material incentives can motivate people to do things that make the world a worse place (selfishness might also motivate a mugger to part someone from her wallet), so can conscience be used to motivate people to do bad things. To understand this, it's important to remember that the "society" in "prosocial" is a relative term. You might sacrifice your own material welfare to benefit one group, while harming another. Think of the self-sacrificing suicide bomber, or the loyal gang member who refuses to "rat out" his colleagues. Indeed, sometimes one's "in-group" might include animals to the exclusion of people (there was a recent case in California where animal rights activists fire-bombed a UC biology professor's house), or supernatural beings to the exclusion of people (violent religious extremists).

So saying that conscience can be used to pursue good policy goals, should not be read to imply that it can't be sadly misused, too. It can. In my view, that's just another good reason we should pay attention to it.