If you take authority, you take responsibility. @nik is right: once @ConnyDuck is in the business of blocking instances, they have a to have a line, otherwise it's subjective and they'll be screwed. I'd say Gab is tame boomer shit compared to half of fedi, so they have their work cut out for them.
Segregating Nazis (if we take it as a given that the people are Nazis) just means the Nazis don't ever have to answer for themselves. Cults and radical ideologies thrive on isolation.
Daryl Davis already got mentioned upthread.
If there are Nazis, and they are as numerous as these people think, what's their plan? Where does this "don't give them a platform, don't ever let them feel safe" stuff stop? Gonna round them up and shoot them? Fuck tankies.
It is not possible for fedi to become less safe due to Gab.