What claim? The claim that people would be more inclined to donate to charity? That should be obvious; if you have more money (due to less taxes), you can afford to donate more. People donate as much as they can to charity already; that wouldn't change, the amounts would.
People currently exploit the welfare state because the government is surrounded by bureaucracy, and they have nothing to lose. A private charity would give to those who most need it, and they would be more alert to exploitation since they have a great deal to lose.
People currently exploit the welfare state because the government is surrounded by bureaucracy, and they have nothing to lose. A private charity would give to those who most need it, and they would be more alert to exploitation since they have a great deal to lose.