Playing Devil's advovate is usually entertaining only in person, or only to the one doing it. If it is not done very carefully, you can end up insulting or hurting someone. I rather prefer to debate my OWN views instead of presuming I can simulate someone else's well enough to make the dialogue meaningful.

And just to take that role myself, how can you tell a "knee-jerk" liberal from a careful, concerned citizen?

(hey...are there "knee-jerk" Libertarians & Devil's advocates?) ☺