It's also a moving part. Worse, a part the customer moves. Which means more opportunity for crap getting crammed in or breaking.
The cover on my laptop's camera is behind the glass. I suppose there is a chance that the slider itself could get damaged, but at least they minimized the exposed surface that could be damaged.
That said, I really can't comment on how durable it is. I only remove the cover about a half dozen times a year.