A really popular (or rather unpopular) one is that women and men are differently capable.
Even with all the caveats in the world (that different means neither better nor worse, that this doesn’t make hiring or salary discrimination ok, etc etc), you’re likely to get in trouble because of it.
However, there are many ways in which we traditionally believed them to be differently capable that were actually that way due to discrimination and injustice.
So, people will be rightly annoyed when someone tries to downplay the effects of systemic injustice.
When we have fixed our systems to be more just and inclusive, only then can we begin to talk about inherent difference.
This is pretty much the perfect example of what is considered wrongthink today, but I have confidence, will be common knowledge in 50 years. This is the example people should be using more instead of the one Altman used (disparaging comments about gay people).
I actually don't have any in mind. I just find it less helpful to focus on the easier examples.
In general, I'm more interested in the underlying dynamics, as well as the processes we use to determine what is morally acceptable or not. I think that looking at the more complex issues and at the ways in which the different viewpoints evolve over time shines more light on these important fundamental aspects.