I've always felt that the proper role of government is to provide services that:
B) services that it would be inapproiate or impossible for private citizens to provide.
Viewed this way, the citizen's relationship to the government is no more coercive then then a citizens relationship to another citizen who is providing a service, and taxes are simply a bill for services rendered. The "violence" associated with non-payment of taxes is no more reprehensible then "violence" associated with non-payment of any other bill.
The only hole in this, of course, is the lack of ability in most countries for a citizen to "opt out" of government services. My brother feels that allowing opting out would be a bad idea. I think I agree, at least for certain category B services that are both very important and whose utility decreases as the amount of buy-in decreases.
P.S. I seem to have missed the introduction of this "PPA" concept. Could someone enlighten me?