[edmundsauto]

It would be a negative for me, because I would need to train my parents to never use this other store. Then their friends will get them to use it, because a sketchy app will be in that store that offers free money, or some other scam. My parents will then breach the secure containment of their phone, without really understanding what they're doing.

It would harm Apple, because when users try the third party app store and have problems, they will expect Apple to support it. If Apple doesn't do the support, it tarnishes their brand to that user.

[gambiting]

Well but that's like saying that cars shouldn't allow mods, because someone will convince your parents to install aftermarket mods and they will mod their cars and crash and die.

Like, sure, it can happen. But if your parents can be convinced by someone to install a 3rd party store and download something from it, they can be equally easily convinced to go to a dodgy website that will scam them from something else and their magical iPhone won't save them from it. Besides, the whole idea that adult people should be prevented from having choice for their own good is almost offensive to me, like ....don't we believe in personal freedom and choice? Your parents should be able to choose to lock down your their phones(or you can do it for them) but equally, if they want to unlock it - they should be able to.