This approach is a lot closer to Android. You actually can still run whatever you want... just the default security settings don't allow it.

Which, for 99.99999% of actual users will mean they are blocked. Digging around in the guts to enable "Developer mode", with all the scary consequences, is not something users will (or should have to) do.

Clicking through a few pages of options is EXACTLY the level of discouragement needed for users who really shouldn't be touching such things.

That's a terrible idea. Menus shouldn't intentionally be designed to be user hostile. Instead just give a warning message, preferably one that is actually informative and appropriately scary looking.

There is a middle ground between letting any malware on the machine install whatever extensions it wants with no user consent, and banning users from installing extensions entirely.

> I really don't get how abuse of a feature is grounds to remove a feature.

If you do the right thing for your users first, this is what you do. You put user needs over developer needs.

Huh? Where does it say they're disabling developer mode? How else would one develop an extension?