I don't know if it's especially threatening when they think it's undeserved or if they just try to frame it as undeserved so they can keep to their morally suspicious ways.
It's the same thing. You are not a bad person for not giving, but your brain notices a problem, and you do not act on it. Whether it makes sense or not makes no difference: it makes you feel bad, and your mind associates this unpleasant sensation with the person you crossed path with at that moment. Then you react: mocking, irritation, etc.
We all do it all the time. It's not about being veggie, or giving money. The topic has no importance at all. In fact, morality has no importance at all. It's the same thing when you don't take the garbage out or have a huge pile of emails, except you got a person to blame other than yourself.
I don't like the moral policing of any group. But there is always a choice to politely say no and go on with your live. Everyone has there own values.
I don't agree on the moral witch hunt that followed either. Take his private email, reframe it in the media. It destroys a person and I think that is very wrong.