Here is the Stewart-Goldberg interview.
Let me say here that i do not really care about the historical connection between socialism and fascist. Was Mussolini a fascist or socialist, an Italian or a European, do not care. I do however care about what socialism is today, how is it applied and its end goals. It is helpful to look to the past when people aren't forthcoming about where they stand but say they are a or b. Or if you are trying to look at what works and doesn't.
I am not a historian and do not have to time to figure out who's wright or wrong. if there are inconsistencies in his book its not for me to say. I haven't read his book. I think if there are some academic problem with the work then so be it. In general if the ideas are interesting or make connections in you head from one thing to the other then its all the better. If an idea comes along that explains better or makes better connections good I'll take a look at that.
Here some of the back and forth if you want to go through this rabbit hole. Salon has an interview with him. Whatever with some thoughts. If you found this I sure you can find your way to get stuck in this rabbit hole.