Would you trust proprietary software to encrypt your communications?
But it shouldn't be. We, as developers, shouldn't harbor any ill will toward the OP should he decide to pull the open source version and sell it for profit. We certainly shouldn't advise him against it or recommend an alternative open source license that better guarantees that nobody can make money off this excellent piece of software.
Geeks like us tend to have a natural aversion to making money by selling our work directly, as though it's somehow dirty or wrong in some way that we can't quite articulate.
But we need to get over that.
We have a guy here (patio11) whose job this normally is, but he seems to have taken the morning off so I'll do this in his place:
On behalf of the Internet, I hereby grant you, the developer, permission to charge money for your software.
There, you're good.
Not everyone gives a shit about making money from the software they write.
There are many reasons to write software. There are many reasons to not charge for it. Stop presuming to know whats best for the developer.
Did you consider the possibility that the author already has a job that pays him extremely well and that the ROI he gets in spending time providing customer support/marketing for a commercial iOS app is actually losing money for him?
You should save the "you are allowed to make money" talk for people who are actually trying to sell software and doing it badly (Because they undervalue the work they created) instead of directing it at someone producing what looks like a labor of love and is not interested in marketing everything he has ever created.
I think that's more a rationalization that developers use to convince themselves not to charge for their stuff than a reality. I've certainly never experienced any support/marketing overload with any of my products.
He already has the app in the app store. His support/marketing is where it is already. All he need do is tick a box marked "allow people to send me money" in his app store control panel and he's done. In short, there's no "down" for the app to go. It's already maxed out on the "losing money" front, and doesn't seem to be overburdening him.
On the customer support side, he might actually see that go down too by charging. Here's yesterday's discussion on exactly that:
http://news.ycombinator.com/item?id=4376126
This really is a case where there's no downside to charging money. And, seemingly, a very real downside of keeping it open source.
Presumably because that's your full time job?
There's a reason I promote the lifestyle. Having a little pile of software products paying you a full developer salary in exchange for answering a few emails a week is a pretty good place to be.
What is the downside of keeping it open source?
As a user of proprietary software, you can't inspect that code for bugs and you can't inspect it for malicious code - you just have to take the vendor's word for it that "it is really secure, honest! And there aren't any backdoors put in by the US government/china/whoever"
I don't know whether chatsecure is any good or would withstand attacks by a nation state, but if I were a security researcher or an aid organisation in the 3rd world, I could look at the source and find out.