It cripples functionality by
blocking scripting, which is a major part of the web.
Obviously you can make exceptions, but then you have to
trust those exceptions, which kind of goes against the idea of making the browser secure in the first place. The point of a browser being secure is that things can't exploit it, not that the user is trusted to tell whether or not a website
might exploit it. If the user has to make a decision on whether or not to trust a website to actually run scripts, that is not a method of "browser security".
Does it help security? Sure it does. But it doesn't make the browser
itself secure, it just helps the user avoid content until he thinks it
might be fine to view.
The goal of security should be that you can view sites in their entirety without losing functionality, and things like exploits and malware are rendered ineffective. The goal is not to force the user to decide whether or not he wants to take the risk.
Don't get me wrong, I'm glad things like AdBlock and NoScript exist, but they're simply not relevant to the central question of whether or not the browser itself handles things in a secure manner, good tools or not.
Indeed, what kind of functionality does it cripple?
IE is, and will always be, a nonexistant part of my daily software use. I don't even use it to download a new browser.
That's great, but it really
isn't that bad. You're being paranoid.