A fluorescently lit group room, resplendent with a two way mirror, a video camera and a microphone hanging from the ceiling.
This is hardly an environment that readily inspires great banter, deeply considered thinking or for that matter, honesty.
And consider a standard 1.5-2 hour group, with 6-7 respondents. Each respondent only gets an average of 10-15 minutes air time (after introductions, warm ups, etc). Throw in a few relatively vocal participants and notwithstanding a switched on moderator, that air time shrinks again.
Even if respondents are thinking deeply about the topic at hand, within this context they may not get a chance to, and nor may they want to, share it with the group.
Again, it’s a compromise.