At the simplest here's my thoughts.
If I want the mod, I will either download it and don't donate, or if I want to donate I donate not "buy". If it is buy via steam I look for it elsewhere. If it is not elsewhere if it offers something that can be replicated I make my own version myself.
Either free download or make it yourself. Donations are optional and you shouldn't feel obligated. Would I like to be paid for things I do? Sure, but my skills are no wheres near good enough to make it worth money. Even at that I'd leave it to the person... it's why I enjoy twitch streamers who either don't have donations pages or have one there and if you feel like donating, if not cool. This shouldn't effect people as much as it does. There are however problems on the development side that worries me(the actual developer who makes the games) and that's where I'm more concerned over.