Yep, but the whole point about anonimity on the net revolves directly or indirectly around freedom (of speech).
An anonimity service is provided to allow people to express their ideas (wrong as they might be) without fear of retaliation .
By - more or less - preventing "right wing extremists" to express their "weird" ideas they contradict the base premise.
This is not entirely different from some (still queer in my opinion) "free" software licenses, prohibiting the use of the software to (example) members of the US government or military, it is simply not "free" anymore when such clauses are given.
Here, as always happens when there is a discretionary choice involved, is determining what qualifies a "right wing extremist", and whether the ban applies to the person/member (and to his/her political ideas) or to the content, let's say that you are a "right wing extremist" that wants to put online a set of cooking recipes, should you be prevented from having a domain there?
Or is it when in the recipe for some stew you make a not-funny reference to "kosher" meat being not suitable?
And who determines if that is only "not-funny" (maybe it is actually funny) or if it is a non-acceptable pro-Nazi hint?