Everything comes down to personal choice. But it's good to remind people that working for free only serves to enforce the belief that the skills we have worked to perfect are of no value. When you work for free it only increases the expectation of others that they too should get something for nothing too.
I try, on most occasions, to refrain from responding at all to freebie requests. But on occasion I'm guilty of replying in what some might term a sarcastic fashion. It's not a good excuse, but when I do it's because I find the request itself to be insulting. Enough said, it's just my opinion...and everyone can an will do as they please.