I think it’s perfectly possible to play ‘devil’s advocate’ on the SDMB. It allows for the exploration of opposing sides and for a greater understanding as a whole. Frankly, it would benefit most of our debaters to be forced to try to justify their traditional opposition every now and again.
What is NOT permitted, however, is the choosing of sides and arguments solely for the purposes of stirring up trouble and causing hard feelings. That would be trolling. Making an argument just to cause commotion is strongly contraindicated here.
So…best practices? When one is playing devil’s advocate it’s best to label it as such. “I’m not sure I agree with this but I can see an argument…” and so forth. Make sure that all involved know the reason you’re taking your position and use it as a means to examine all sides of an issue.