'm not ashamed to say that my first thought was: can I profit?

And indeed, there is no shame. Nearly all software is written for profit in some sense. Sometimes it's monetary profit, sometimes the new software relieves you of tedious, boring work, sometimes the profit is fame (or XP on perlmonks ;-).

As a hobbyist I mostly write programs because I want my job done (and because it's fun). I publish the more useful programs as open source because that usually implies getting feedback and helpful feature suggestions (I'm not creative enough to think of some of the really useful features myself). Plus open source projects really bring traffic to my websites ;-)

One of the reasons not to sell my software is that it puts me under a kind of mental pressure: if one of my customers buys software from me it just has to work. IMHO. And I don't think I can guarantee that, so I feel like I'm cheating when I'm selling something that just might not work for the buyer.

But I still profit from my software, mostly in terms of skills. And that pays when I do contract work.

I hope that I'll never have to make money from selling software because I think it would kill the fun.

(As a side note there are other, ethical reasons for me to publish my software as open source, but they don't belong here.)