It isn't yours, because however mandatory it was you paid it to them, and when you give it it ceases to be yours. At any rate even the richest among us are making comparatively miniscule contributions in the scheme of things.
There are plenty of things the government does that I like, and I would sure like to pay for those ahead of say, funding for wars I don't like or finding new and indirect ways of killing people (by this I mean military spending), but I pay my taxes with the understanding that this is all part of the deal.