I personally prefer Winner's motto: "Tolerate those who want to tolerate us". If there was one -ism thought I could irradicate from people's minds it would be racism, and I can't tolerate racists in any way shape or form. I find it deeply perverse when racists march under the banner of freedom and democracy, and I have no moral objections to the government using our principles and morals to ban them from doing so. There should be no place in society for racists, and anything that would erradicate that which has plagued Europe once before I would welcome with open arms.
I certainly don't accept the "slippery slope" arguement you presented. It simply wouldn't happen that a good man's freedom would violated. The law specifically targets racist Nazis, and would not set a precident (sp?) against other political movements.