It's not an assumption, it is good manners and one of the Ten Commandments that underpins our entire society - do unto others as you would have them do unto you. So when someone gives me something for free, I take their example on board and do the same thing - I do unto others as has been done to me. Someone gives me something for free, I give something of my own to people for free.
And I'd be very surprised if you never used any free software, samples, or whatever in your music production.[/quote]
Which is fine because I have never earned a penny from them, either. I spend at least 4 or 5 times more than I make form music. e.g. We got paid the handsome sum of 576 Euros, after tax and accommodation, for playing at Wave Gothik Treffen in 2017 but the trip cost us around 4000 Euros in total. What I try to do is acknowledge every act of generosity in a meaningful way, either by reciprocating - also making free stuff available - or putting an acknowledgement somewhere in the liner notes of a release where I have used something I got for nothing.
How many times have you paid for donationware? I get the impression not many people do it, given that the FBM guy made the effort to email his thanks to me and seemed genuinely grateful, like it was a most unusual occurrence.