If you take my gift and profit, it doesn't hurt me, there were no strings. Your users presumably benefit from the software I wrote, unless you're using it for evil, but I don't have enough clout to use an only IBM may use it for evil license. You benefit from the software I wrote. I've made the world a better place and I didn't have to market or support my software; win-win.
I've done plenty of software for hire too. I've used plenty of open source software for work. Ocassionally, I've been able to contribute to open source while working for hire, which is always awesome. It's great to be paid to find and fix problems my employer is having and be able to contribute upstream to fix them for lots more people.