I can sometimes see the necessity in selling a firearm, especially one that does not have much sentimental value or does not see much use. But for me, I have never sold a gun and I never plan on it either. I say that I don't plan on it, but you never know what circumstances may come up. My wife and my son come way before any material object.
Most of the guns that I currently own are guns that have been in my family for generations or have some kind of special meaning or memory and I would have a VERY hard time letting something like that go. All of my guns see use and are, for the most part, well taken care of. They have been passed down through my family and I look forward to one day passing them down to my son (along with a few more aquisitions along the way).