They were probably also against Window's UAC popups.
They were likened to California Prop 65 warnings: so prolific as to be ignored, and arguably causing more harm than good, because just as apparently since EVERYTHING causes cancer one can't make decisions about avoiding things that actually do, so to does EVERYTHING trigger a UAC popup and so who gives a fuck, one more thing to quickly ignore and click through.
And we wonder why Microsoft sucks so bad at securing Windows.
These days you mostly see the prompt when you're installing or updating an app, which makes a lot of sense.
What I mean is, this is Microsoft's fault so far as users got in the habit of running in admin in the first place, but I doubt you would've been able to do better given where Microsoft was with its software ecosystem going into Vista.
As a sister comment mentions, it's akin to warning the user whenever they run a command under su/sudo.