Two additional comments:
1) I have been assuming "combat" is used in this case to draw attention to the difference in complexity between most social interaction rules and most combat rules,
not to suggest that encounters should have to be adversarial.
2) I'm never going to pretend to be convinced of something just because the DM tells me that's what my character thinks. While that type of roleplaying is certainly a valid, it's just not very interesting or fun for me. If the adventure depends on me pretending to not know something, it was a poorly designed adventure.
The exception, of course, is if it's some kind of magical compulsion, which would presumably have a finite duration. And that distinction illustrates why I don't like the sort of roleplaying that
@zarionofarabel is advocating: playing a character that has been
permanently mind-controlled, for an entire campaign, would be (to me, anyway) not very different from being forced to play a character whose thoughts and beliefs are dictated by DM and dice.