I fully agree that calling a few people stupid is not the same as calling a group stupid.

However, I question whether calling people stupid at all--either directly or indirectly--is either fair or wise except after evaluating the particulars, especially when those people also have presumed competence. It's a pretty strong statement. If the shoe fits--sure. But a blanket rule of, "If you're not with majority opinion, you're stupid," seems like overkill.

As a general guideline, sure. If you're going to bet with or against the majority, and you have no other information, the majority is the safer bet. You didn't phrase it as a guideline, though; you phrased it as an evident truth.

But it's all too easy to find examples where the conventional wisdom is wrong, and you don't find out when you start by belittling the people who take a contrary stance. And even if conventional wisdom is correct and the contrary voices are wrong, belittling them is not usually a good way to open their eyes.