I believe the reason we need to coerce people into paying is because economically if you don't let people volunteer to pay, it just doesn't work. Excuse me if I don't have the sources for this as it was my Econ PhD friend who explained it to me.

I wonder if the argument against it is something like this: imagine for every person, they have some amount they are willing to contribute to said scheme. However, unless the total amount needed to fund such a project is small, if you don't force everyone to contribute then the cost will be significantly higher per person. Then, because it's higher than what some people want to pay, they choose not to pay although they would have otherwise. After that happens, the price increases more, and this effect continues.