I think this isn't a great decision for two reasons. Firstly, the merits of the specific case. While I think anti-Zionism in general is a perfectly defensible position (indeed, people would probably consider my stances on the Israel-Palestine conflict to be anti-Zionist, though that's not the label I'd use myself), Miller goes well beyond this into obsessive conspiracy theories.
Secondly, the broader tendency of how judges have started interpreting what constitutes a protected "philosophical belief" recently. Even if I fully agreed with Miller's views here, I don't think they should qualify. The inclusion of "philosophical belief" alongside religion as a protected category in the Equality Act was intended to cover belief systems which it wouldn't be accurate to describe as a "religion", but which work in a somewhat comparable way - namely, that they significantly influence how you live your life and see yourself to the point where they are a fundamental aspect of who you are. A prominent example would be veganism - it's not a religion, but it's a belief system that significantly impacts how you live your life on a day to day basis, and essentially sets ethical rules for what activities adherents consider themselves permitted or prohibited from taking part in. But in Miller's case, as in the case of Maya Forstater before him, judges have expanded this to include beliefs that are not really in any way comparable - beliefs that are essentially just political opinions.
Now, I'm not saying I think it should be legal to simply fire people for their political opinions - there should indeed be worker protections on this. But I don't think that should be at the same level as protections for discrimination on grounds of racism, sexism, homophobia, etc. And as I said, mere political opinions are not what the Equality Act was intended to protect.