IMO then the people happy to contribute to such a system would mostly fall under 1/2 (under the assumption that one's motivations are altruistic and not centere

IMO then the people happy to contribute to such a system would mostly fall under 1/2 (under the assumption that one's motivations are altruistic and not centered on the communal benefits they also receive), but the people who aren't happy to contribute would not qualify (at least, not via their taxes alone -- there might be other reasons for rejecting taxes, and they might contribute elsewhere in a way that still puts them in the 1/2 category).