If there's no compulsory tax and you're living in a village and the village board want to build a road, they have to present this idea to all villagers. People who feel like a good idea will contribute to it.
But if the village board tells them they want to send a couple of soldiers to a country, you've never heard of, how many people will contribute?
Income tax in the US:
https://en.wikipedia.org/wiki/Legal_history_of_income_tax_in_the_United_States
I don’t think that that would work though. People could choose to not contribute to build the road but still benefit from the road after it was built. It would become a game of chicken to see who could get away without contributing. And it’s terrible for poor people; they have the least to contribute but the most to gain from it. In this road example, rich people could afford to continue to pay their way around the inconvenience of not having a road, while the poor could not do that. If taxes are collected from everyone, then everyone pays for the service that they all benefit from.
