I write a column for a local newspaper. I might spend 2-6 hours on the column. They pay me 30 bucks. My real work pays me a bit more than that :-). But I don't consider my writing "charity work" because I'm not really GIVING anybody something, I am getting paid to perform a service, just paid relatively poorly.
It doesn't COST me anything but my time, and I give my time to writing because I enjoy writing, and because I like having the opportunity to pursuade others of my opinions.
A doctor who treats patients and gets paid less for it isn't doing "charity", unless she specifically is turning away paying patients in order to treat the charity cases.
I suppose the same is true for you and your indigent work. It costs you your time, but you do get paid, just very little relative to your normal compensation. If you turned down paying clients because you don't have time because of this work, you did lose money. But if you took those clients, whoever ended up NOT taking those clients would have more free time to work cheaply for the indigents.
The only way the "cheap lawyers for poor people" actually can be considered "charity" is if there are so few lawyers in the world that there are paying customers who never get a chance to have a lawyer because the lawyers are too busy doing "charity work".
Otherwise, it's just a business which already is operating and realises that making less money is better than making no money. Like a store that does a sale.
You have summarized my point very well. I make very little on these cases but, I am really just putting in extra time.