> It is a crazy concept, because taxes are coerced by governments under the threat of violence, whereas the freedoms of FOSS software are intended to be entirely non-coercive.

In doubt, you will have to enforce the freedoms of FOSS by going to a court (i.e. use the governmental "violence enforcement system"). On the other hand, if you pay your taxes "voluntarily", you won't be coerced by the government.

In other words: in both cases threats of violence are involved.