Conservatives believe that charity is only charity if it isn't mandatory. Taxes represent seizure of your assets at gunpoint (no one would pay if the IRS didn't enforce). Forcible asset seizure + spending on purposes which you may or may not agree with is many things, but it is not charity.
In terms of actual charity numbers, self-identified conservatives give a lot more.
http://philanthropy.com/blogs/prospecting/conservative-voter...
Households that describe themselves as conservative tend to give more money to charities than moderate and liberal households, according to a new survey.
In a survey of 3,300 households that donated money to charity in the past 12 months, the company Campbell Rinker, in Valencia, Calif., asked respondents about their political ideology.
Of those surveyed, those who live in conservative households donated an average of $3,255 to charities outside of places of worship during the past year. By comparison, moderate households donated $2,926 and liberal households donated $1,879.
http://blog.beliefnet.com/castingstones/2008/04/conservative...
In his book, Who Really Cares: The Surprising Truth About Compassionate Conservativism (Basic Books, 2006), Brooks discovered that approximately equal percentages of liberals and conservatives give to private charitable causes. However, conservatives gave about 30 percent more money per year to private charitable causes, even though his study found liberal families earned an average of 6 percent more per year in income than did conservative families. This greater generosity among conservative families proved to be true in Brooks’ research for every income group, “from poor to middle class to rich.”