Why are we discussing this in isolation? The term "liberal" has come to describe a whole host of positions that are not liberal at all, nor progressive, unless the progress is in the wrong direction. Oppressive taxation, bizarre levels of gov regulation, gun control, and the list goes on. I will refrain from naming some of the more controversial issues. Gun control didn't just happen to fall into the "liberal" camp; it fits with the larger mindset that views the citizenry as a resource to be managed and herded.
Nitrogen, I definitely agree with your view, and it explains why many conservatives don't get the gun issue, either. But BigJake is more or less correct, as well. Liberal has become a euphemism for "making all things right through government."
I think Nitrogen's view is probably the main reason why most rank and file people think gun control is important. I think fistful's description is closer to reality for the real hard core leftists who push the issue as well as the rich elitist class types.