Firstly, it's debatable to what extent we might say that beliefs themselves are responsible for things - they certainly have a big role in human behaviour.
Secondly, when somebody says that Nazism or communism or whatever is responsible for certain things, it's quite obvious that they mean those people who subscribe to the relevant belief are the ones who actually carried out the actions - which brings us back to pointing that out being pedantry.
Thirdly, you didn't answer my question: how is saying that a belief is responsible for somehow buying into the belief?
No, if you don't think there are external things such as gods causing beliefs, then it is not debatable about how much beliefs themselves are responsible for things. They have no agency. And stating that they have a big role in what happens is a truism here unless you are arguing for agency.
And again, if it is about the individuals then the beliefs are merely expressions of the individuals. The problem with the use of the beliefs themselves as being in any sense responsible is that it views things as being 'leadership's because they are external!
As to your question, it's not about buying into the belief itself, but about buying into the idea that beliefs are externally responsible.