You seem to be assuming that voluntary is more efficient and you seem to be assuming voluntary results in a higher contributions through some kind of adequate participation rate.
Obviously voluntary contributions are more efficient because people resist being forced to do stuff. They evade, avoid, run, hide, and fight back. Monopoly welfare providers also face no competitive pressure to be efficient.
"Obviously"..... yeah, right.. so obvious that you are speculating. just making things up on some kind of logic in your head that sounds convincing to you and to the other libertarians who want the facts to be what you speculate them to be.
If participation is inadequate, we have two options: I prefer persuasion and you chose coercion.
There you go creating my position. Having mandatory, is NOT the same as coercion.. b/c a large majority of the people do NOT need to be coerced to follow rules of their own making and a society of their own choosing and a community in which they chose to live... I would NOT call that coercion. But you want to call it coercion in order that you can knock it down and to show all of its flaws. Your thinking is very incomplete in these regards. Maybe you need to get away from your imagination and meet people and talk to people and you will see that there are different viewpoints out there that need to be accounted... also, that is called listening.
The danger with coercion is that the coercive mechanisms remain in place and can be used for socially harmful as well as socially beneficial ends. Taxes fund war, graft, secret police, etc.
YES... I agree that there are a lot of problems with various ways that tax money gets put to work to carry out dirty deeds. Sometimes the dirty deeds are mixed in with what is arguably justifiable... and yes we do find out about tragedies being committed in our name ... And, some of these may be solved by taking away funding or may be solved by better election procedures or may be solved by greater transparency... there is NOT only one solution to these kinds of negative application of the arm(s) of government.