This wouldn't be truely democratic. It would rather be just like donations. Government spending works, because it's all out into the same basket. If it weren't, then rich taxpayers would move the movey to projects they want - and as would have very little old-age welfare, because they don't pay much taxes anymk6and every group in society would put the money into their projects.

If you can't see the obvious ways this would fail and/or be abused you should steer clear of any and all leadership positions.

Then everyone would just fund things 100% and 0% for everything else they deem not important, like education or roads.

Tax-deductible donations get you part way there.

There’s no point in having a government if you don’t let them decide how they spend and raise money

And if you get caught using a public service you didn't pay for, you get fined.