OK. That has caused me to update my beliefs. I still think that there is relatively little risk -- like, you should be much more worried about being in a car accident -- but I no longer think it's on par with being struck by lightning.
Create a malware (which due to some big company fuckups can be even embedded in a webpage these days). Capture frames indiscriminately. Add some image recognition algorithms (from OCR to machine learning, depending on what you want to do) to flag interesting hits.
Voila. Massive dragnet. Applications can range from simple blackmail (a-la Black Mirror) to industrial espionage.
But, I believe we (as technologists) have a responsibility to use and push for strong security practices. I don't want my kids to grow up in a world where creeps blackmailing them through their webcams is a possibility, or where a rogue politician has all the tools of absolute authoritarianism already set up and waiting for him.
A camera cover is a huge win. It's super easy and cheap (a piece of plastic), it's easy to understand (entirely mechanical), it works 100% when used, and it's failure modes are obvious. Not all security controls are cheap, easy, and 100% effective, but this one is. And if you don't bother to use it in your bedroom, then that's fine, but every webcam should have one.