What are you asking about? I don't support extremist ideology - be it left or right. Extremism and violence was never beneficial to the political discourse or greater public. So i disagree with those ideologies. I vote on laws and elect people which i believe will keep extremism out of our system.
If it comes to the quality of someones work, private conviction does not matter. Sure, they might let personal beliefs bleed into their work. But there the beauty of Open Source comes into play: I can check it myself and if i don't have the capability to do so, many others do.
So if they are on the far spectrum of something i disagree and i am very greatfull for good quality of work they provide for free, i might still give a small donation. If they are actually extremist, i prefer to let the authorities deal with it. Where i come from the police actually cracks down on this kind of people and they probably are better at doing so than me myself.
Just because there will be people who ask about freedom of speech... Someone way smarter than I said something like: "Your freedom ends where someone else's freedom begins". This should be the base rule to identify extremism. So to stay with NAZIs: A far right person who doesn't want Jewish people owning a store infringes on someone else's freedom. Therefore that person is an extremist, should not be protected by his freedom and authorities should deal with them.