As a second-term mayor, Giuliani significantly expanded the size of government and spent at rates far exceeding the rate of inflation (and this is excluding the unavoidable costs of 9/11). Paul, Tancredo, Thompson, probably McCain and possibly Romney are all more fiscally conservative than Giuliani is.
And Giuliani’s problems go beyond social issue — his record on the Constitution is deplorable and makes him utterly unfit for office.
Any libertarian, smaller government minded conservative should find Rudy to be utterly repulsive. He's an authoritarian and has a big government streak in him a mile wide.