Re: when did a third party plugin ever load without the user knowing it was going to load?
Not as simple as that. One of my main jobs is removing crap from client PCs. One of the worst to prise out is the Babylon toolbar from Firefox. I'll get plenty of DV's for saying this despite it being true but Babylon, once installed, is very easy to kick out of IE (The Autoruns tool kills it, stone dead), a little harder to dislodge from Chrome, and a bloody nightmare to remove from FF. Don't believe me? Give it a try. After all, you do believe in FF's invulnerability, no?
So it's not so much about users agreeing to install crapware; it's about preventing it's installation, or removing it from the machines of vulnerable users (usually the elderly, whose thoughtful relatives have installed FF in an attempt to tighten their security a little).
So DV away! I only speak from very wide experience, so waddoo I know anyway?