"You really have to think of yourself in order not to become a charity case yourself. Doing that which is fulfilling and making you a better person has a duplicative effect and amplifies all that you do without the burnout or poverty stricken state that I think this system leads to."

This is a good argument against donating too much, but you can still keep enough for yourself to avoid poverty and burnout while earning to give. For example, of what my wife and I earn this year we'll be dividing the money up like:

50% donations
23% taxes
21% saving
6% spending

You can see we're saving several times our annual spending, which gives us a good safety margin in case something goes wrong. Part of why we're able to have a budget like this is that we (me, wife, daughter) live frugally, and part of it is that we've tried to earn more so we can give more.