On a laptop you CAN'T manually disconnect the webcam and mic.
Even on some desktops it's a major pain to reach around under a desk to the back of the box to disconnect a webcam.
And the last thing you want to do is get glue all over an optical lens. Especially if you DO have occasional use for the webcam.
And finally, virus scanners are FAR from perfect. They allow more crap thru than they protect against on Windows boxes.