I agree that extension security isn't considered nearly as often as it should be, though my barrier isn't quite yours. For me, it comes down to developer trust

I agree that extension security isn't considered nearly as often as it should be, though my barrier isn't quite yours. For me, it comes down to developer trust and permissions. If someone I trust wrote a small, feature-targeted extension, I would probably be comfortable installing it. Similarly, if the permissions an extension has are tightly scoped to its use case, I'm more comfortable installing it. Now that I write that, I'm not sure how permissions and upgrades go together. If an extension that had tight permissions relaxes them I'd get notified before they took effect, right?