What social contract? Good, so you admit that the social contract is not valid.
Then, if there is no social contract, what right does anyone or group of persons--whether they call themselves the mafia, the government, or just a random group of bandits--have to take your money without permission?
I'm not asking you if society is overall better or worse off if the money is taken. I'm asking from where do they take their authority to take your money? When has the citizen explicitly authorized it? If I take a million dollars from Bill gates at gun point, then 50,000$ each to 20 random homeless people, then there is no argument that I have just raised the standard of living amongst the 20 homeless people, while not affecting Bill gate's at all, because he's insanely rich and 1 mil is nothing to him. However, just because that would help other people does NOT give me the RIGHT to rob Bill gates at gun point. Regardless of how good my intentions are, I do not have the right to take his money, even if I think I will spend it better than him. It's still HIS. This is essentially what taxation is, in several ways.
People say it goes to good causes: schools, roads, and the such. But the means by which it is taken is immoral. Taxes are collected, and if you don't pay you will be arrested and thrown in a cage. If you resist arrest, police reserve the right to physically harm you and force you. If you resist even further, they reserve the right to shoot you. That's what taxation is. Now, does it come down to killing someone every time they won't pay taxes? No, 99.999% of the time it doesn't. But the use of lethal force is the bottom line and WILL be used if the other coercive/immoral means are not used. Policemen carry guns for a reason: the law is enforced at the point of a gun. The law is you have to pay your taxes. This is why taxes are immoral, as well as laws. These mechanisms of "pay or violence will be used" are the exact same extortion techniques used by the mafia.
You go on about the "haves and have-nots" and how the have nots will take from the haves. Show me a society where this doesn't happen? The have-nots always take from the haves, in one way or another. Taxation and welfare programs? Corporate subsidies? Social security? Medicare? ANY redistribution of wealth by the government is the have nots taking from the haves. Just because it is done under the guise of legislature and laws doesn't make it any more moral or less barbaric.