[chimprich]

> I hope the vast majority of people would stump up that kind of cash in the absence of any other taxation.

This is, in my view, a pretty naive (maybe to be polite I should say highly optimistic) view of human nature. Even if a majority of people planned to pay it I suspect many would end up not paying it most months as other priorities intervened.

Even if, say, 60% of people did end up paying the voluntary "taxation", a large number would pay nothing. The total sum required would be the same and those willing to pay would have to pay significantly more or there would be a huge shortfall. This would be extremely unfair; freeloaders would get a huge effective pay rise and consequently more influence in society.

In practical terms it would be very difficult to pay for services if if it was not possible to predict how much tax was to be gathered from month to month. Government income would fluctuate wildly. Employment in the public sector would be very risky. The economy would be extremely volatile to say the least. Planning for the future would be next to impossible.

There are many more ethical and practical problems with this idea. I could go on.