> Then the rule is just pointless. Can anyone prove that you are not sick
No, but if someone goes into a tournament, resigns on move one, and then goes to Twitter with a tweet saying "if I speak....big trouble" then in that situation they can be punished.
Is it hypothetically possible that someone might be able to secretly pretend like they are sick?
Sure. But the point of rules like this is to prevent the highly obvious and damaging examples of unsportsmanlike conduct.
If someone is secretly resigning games in an unsportsmanlike manner, but nobody notices, then there isn't much actually damaging about those actions.
> should there be a rule that forces you to play
No, instead unsportsmanlike conduct should be punished. Such as resigning on turn one, and then going to Twitter about it with a vague accusation.
> My point is where do you draw the line?
Well what you do is you punish the really obvious stuff.
And if it is done super secretly, then it isn't that damaging anyway, and we don't have to worry about it.