At the moment people argue about whether or not XYZ should have been posted here because it didn't happen on ebid, though, so I don't quite follow why arguments would necessarily increase?
I'm not proposing a change in the rules about personal attacks, swearing, bringing the site into disrepute etc - so why would bickering be worse? If we can talk about ABC without too much bickering, why not XYZ?
I don't understand why allowing a discussion about selling elsewhere would change that. I think politics and religion are far more contentious and would rather see those banned than selling sites.
I don't know why you think that. Why would we be less capable of discussing a problem with a sale made on BIGOLSELLINGSITE politely than we are here and now?
Note: not saying you're wrong, just don't follow the argument yet and would like to understand why you think it would make that difference.