It depends on what the alerts are. Honestly, I don't think it's safe to assume they are harmless.
Most people keep their phones within reach every waking hour. Not to mention, when someone's phone makes a noise, they pretty much respond immediately. As far as propaganda tools go, this will be a real nice one.
Yes it will be. It's only the beginning. They will work their way to it being mandatory on all cellphones. Then all TVs and radios. It's a government takeover of communications.
I agree with you that people shouldn't have to listen to these messages (or at the least they should have the option to turn them off) when they buy an Apple product but I disagree with you that this is totalitarian.
Totalitarian is state run media like in NK or beaming in a constant stream of Big Brother on your television like 1984. I can just not buy this product and I won't have to see the messages.
Cellphone privacy is not a right guaranteed by the Constitution, and in this case, it's a private company voluntarily selling out their loyal customers.
The presidential alert on the WEA system would be the same as activating the national broadcast Emergency Alert System. The same national EAS system that in fifty years of it's existence, through four major wars, two presidential assassinations, and a major attack, has never been used.
Local emergency alerts (mostly life-threatening weather alerts from the NWS and AMBER alerts) are optional.
Calm down.
EDIT: I should also say that in most jurisdictions, your local emergency management office has Reverse 911 to call all landlines in case of emergency. I've seen it used where I live during the aftermath of a hurricane. This is similar, except in text form.
That's one of the reasons why I use Linux instead of Windows or OS X. Linux is open source and is very secure. The others aren't open source and it is much easier for Microsoft and Apple to leave holes in them on purpose so they can spy on you.