Great idea except that you just enabled anyone to delete all your data without your permission.

That's the whole point. If someone gets physical access to my phone, I don't want them to get access to my data.

But what if someone picks up your phone at a party while you're just a few feet away, and they decide to be a dick? It would take them just a minute to erase all your data.

It's all backed up to the cloud, so you can restore it all

Which defeats the whole point of trying to secure your data.

You can have a long, secure password on your backup, and a short pin on your phone

How? Because if the OS-manufacturer has access to my backup, that's not secure? What?

The phone stays in my pocket.

Worst case: restore from backup.

Who leaves their phone sitting around at parties?

Lots of people.

If they are worried about bad guys deleting all their data, they should stop leaving their phone around at parties. Getting their phone stolen is an even worse outcome, because the data is effectively deleted and the hardware is gone. And it's strictly easier than stealing the phone, deleting the data, and returning the phone, which is what the ggp comment was suggesting we worry about.

Don't have little kids, eh? I've given up on lock codes to keep them off it because they'll make it lock up for hours, backfiring on me many times.

I think I knew this wasn't just a problem for me, but it's nice to see it confirmed by someone else.