Bad idea, perhaps. But why should Apple get to determine what is or isn't a bad idea for one to do with their own phone? (Although I would suspect part of the reason they banned it is to avoid claims of "Apple's so greedy that while they ban so many legitimately useful apps they allowed this one, just because it can break phones resulting in added profits for them from people buying replacement phones".)

Because, Apple is warranty liable for selling an app that basically get you to break your phone either via current replacement plans or the expected lawsuit. This is a money loser and a problem for parents.

Apple rejected the app. Did you read the article?

Yes, I read the article and knew they banned the app before leaving my comment. I agree with their position and further added why. Should is often used as an agreement with an already taken position.