Even though I agree the term has a nice ring to it, I don’t think the term Ultra-Capitalists is a good idea since the mayority of the people sees capitalism as corporatism.
I think ‘Anarchism’ is just fine, since it is defined as a political theory favoring the abolition of governments. It has nothing to do with the abolition of hierarchy, and everything to do with the abolition of the state.
If i reallt had to think of a substute term, I’d go with State-Abolitionism; It has a positive sound to it, and since the term was used to end race-slavery, it can be used once again to end tax-slavery.