Income distribution can be seen as a discussion on what is "proper" or "safe" in a society.
I hope you realize this is a very subjective interpretation. You could make the same reasoning with abortion, death penalty or anything. I'll get a godwin point if I say it, but German people at some point in history considered it was "proper" and "safe" to ostracize jews.
To you it's "proper" and "safe" to redistribute income. To me it is just theft. And theft has nothing to do with hygiene (or whatever you mean by "proper") or safety.
If and when a majority thinks that it would be right thing to do, then it becomes a social convention by definition and the Argumentum ad populum logical fallacy would not apply to it.
A social convention is NOT what the majority thinks. The "Argumentum ad populum" article does not define it this way. You need much more than the majority. Otherwise polemic topics such as abortion could be considered as social conventions, which they are obviously not.
If you say that an idea is true because a majority of people think it is true, you do not say it is true because it is a social convention, you just say it is true because a majority of people think it is true. That's all. And this is precisely a
Argumentum ad populum.