> Or would you only want to do it if everyone at your income bracket was also doing it?
I think this is general answer to this question (at lest it's mine). It's similar to prisoner dillema: I am happy to agree to rules forcing cooperation but in absence of those I won't cooperate that happily (reasons I think are easy to imagine and I've just seen that one poster did great job explaining those).
It's not "I want to give away half my money", it's, "I want to live in a society where all people give away half of their money, and of course I am willing to be subject to that rule myself."
The purpose of government, if it can be said to have a purpose at all, is to cover those items where we're better off doing them but they wouldn't happen on their own due to various game theory considerations or just plain transaction costs.
I think this is general answer to this question (at lest it's mine). It's similar to prisoner dillema: I am happy to agree to rules forcing cooperation but in absence of those I won't cooperate that happily (reasons I think are easy to imagine and I've just seen that one poster did great job explaining those).