In some cases, government impedes charities (Katrina, for example). I believe that people would give much more to charity absent confiscatory taxes. Also, some people just believe that it IS the government's job to provide these services.
I don't see how the gov't presence in N.O. stopped charity from coming in. Various charities may have had to find the gaps that the gov't left or rerouted their help when required to do so, but no one was told not to send aid or open thier homes to Katrina victims.
And I don't believe the second post. First of all, as a whole, we don't pay that much in taxes (and this is coming from a person who got to pay 14K just in capital gains in '05). The amount we are taxed should not impact our charity. My family gives 10% no matter what. So do I. I also donate time, clothes, and the occasional canned food item. I have never considered using the fact that I, like most other Americans, pay taxes and therefore have no responsibility to give to charity. Anyone who uses this excuse is not going to have a charitable heart anyway--it is either part of your belief system to help others or it is not.