This was brought up when trading was legalized, subject to certain restrictions. Opponents of legal trading would argue that it'd be difficult to make kingdoms respect the legal rules.
Let's say a kingdom is formed in a single round through illegal trading, on basis of a shell. 25 players join the kingdom and set about playing. Let's further say they go and win the land crown or something. Do you consider this foul play, and do you consider them unworthy of the crown?