Check the exceptions on the wikipedia page you linked to. Income redistribution falls withing the lines of social convention and safety, therefore the fallacy does not apply here.
The section on social convention is about what is polite or proper. The given example is about russian people kissing each other. I read nothing about income redistribution.
You say it's a social convention. It is obviously not as consensual as you suggest. This very debate proves it.
Income distribution can be seen as a discussion on what is "proper" or "safe" in a society. You are absolutely right about it not being consensual, and I actually have no hope in seeing the system implemented in the near future. This forum topic is more of an intellectual debate rather than a call to arms. But people's ideas change over time. 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.