I won't put up with a grumpy child who stayed up all night
My point, really, is that these emotional reactions shouldn't be avoided at all costs (i.e., "you shouldn't or can't because you might"), but rather seen as emotions or expressions which need to be supported and nurtured should they arise.
To be even clearer we should separate how we approach what a child wants to do from the consequences of what they do and treat them as two separate issues.
Sometimes what a child wants from an experience will be worth the consequences. But they'll still need help handling the consequences.
I'm thinking of a child staying up all night and being grumpy the next day. We shouldn't prevent them from staying up all night because they'll be grumpy. Being grumpy may be a small price to pay in order to experience staying up all night. The grumpiness, if it's bothering the child or causing them to harm the rest of the family, can be handled as a separate issue.
Or a child might choose to play a fascinating video game to the point of being testy from inactivity. The solution isn't to limit the video game, but help them figure out how to deal with the consequences.
His behaviour worsens from watching a lot of TV and he gets headaches.
We shouldn't see our purpose as preventing kids from making decisions with bad consequences. We should see our purpose as helping them make decisions.
So a child who gets cranky and headaches from watching too much TV needs help deciding what to do about the consequences.
What if a kid got cranky and headaches from reading all day?
(That might not be a good analogy among conventional parents. But I hope people here would see reading all day as a good thing :-)
Would the response be to limit reading?
Or would a better response be to help him see the connection between something that's causing a problem with him or the family and what he's doing while reading (too inactive, a position he's frozen into or whatever). And then come up with ways he can handle that. Maybe he'd choose to read less at one sitting. Or move around while reading. Or set a timer. Or ask mom to remind him to move. Or decide it was worth feeling cranky but work on ways to not snap at family members. Or ...