If I had to guess, given his character, I would hazard something along the lines of "if you have the opportunity to make the world a better place, then you have

If I had to guess, given his character, I would hazard something along the lines of "if you have the opportunity to make the world a better place, then you have the moral obligation to". If he were in a position where he wanted to commit suicide, it would be the "easy way out" - analogous to continuing his easy life in Hawaii, instead of throwing it all away out of duty. Of course one can contrive scenarios where suicide is "the right thing to do", but I doubt Snowden expects to find himself in such a situation.