Yours is an interesting, but unrealistic hypothetical. In practice, I do not know of any player who would be interested to make the agreements you are worried about.
But just to play along, let me ask you what you think a TD should do in the case of the former, the case where players agree not to double. Should he post a monitor on the match, and then have him interrupt a game to announce that a player must double in a certain position? Are you suggesting that we need a rule that requires a player to double when it is in his interest to do so? If so, what does that mean? How would you determine that the rule had been violated?
Perhaps you would suggest that we need a rule that explicitly forbids an agreement to not double. That would be a solution to a problem that does not exist. If you really think we need that rule, perhaps you think we need a “Tanya Harding” rule as well. It should be against the rules to have your boyfriend hit your opponent in the knee with a steel pipe.
Steel pipes are bad. I don’t think a TD should allow them.