My current rationalisation for my level of charitable giving is "if, say, the wealthiest top billion humans gave as much as me, most of the worlds current problems that can be solved by charity would be solved in short order".

I use this as a labor-saving angst prevention device.

Me: "Am I a good person ? Am I giving too little ? How should I figure out how much to give ? What does my giving reveal about my true preferences ? What would people I admire think of me if they knew ?"

Me: "Extra trillions thing. Get back to work."