I really don't understand why more people are not getting this.
It can be plenty consequential in the real world, I said from the start of this thread that someone could be arguing a popular opinion that nobody in the room happens to hold.
This happens all the time in silicon valley as an example: a bunch of educated, comparatively wealthy, mostly white men make decisions. Maybe they are not very in touch with the opinions of the vast majority of humans who fall outside that category. What I am advocating for this case is the ability to have empathy for those who are unlike you, step outside your biases and adopt an argument that is not your own. This is a good skill. People are falling over themselves trying to call that lying and universally bad or nearly so.
With parenting - I see no issues. And I do use such an approach, but my spouse, I believe, trusts me.
So... It looks like the problem is - when the debate is used to judge world view of the person to decide if one would like to trust them - such "devil advocate" arguments are harmful. I believe it is just one possible use of the discussion, but I will keep in mind that and try to avoid arguing from some other perspective if I see the person is trying to figure out if they want to trust me or not.
But if the discussion actually influence real-world decisions then it matters a great deal what people actually believe.