At which point it's already too late - the hacker has had access to your camera for some period of time, until you notice the light. If you're interested in stopping people seeing you then you've failed. Putting a hardware block on the camera (eg tape) before you're hacked means that the hacker won't ever get access to your camera to see you.
The hardware block is about stopping people accessing your camera. It has no effect on anything else.
Regardless of what you do with your camera you still have to defend against other ways you can be hacked.
Yeah for like 10 seconds. Who cares? The problem with webcams is they can spy on you for days and weeks on end, and record your sensitive conversations.
"Hey Siri" works on desktop devices: https://9to5mac.com/2016/07/15/how-to-enable-hands-free-hey-...
"Okay Google" was removed from desktop: http://www.theverge.com/2015/10/16/9553051/ok-google-removed...
I think that having the mic light always on when you enable voice activation, would go a long way to showing consumers the risks of it. It makes it visually obvious that you are being recorded.
If you just block the camera you won't know that your computer is being hacked. The piece of tape isn't going to stop the hacker from doing much. Knowing my computer is hacked is far more important than stopping the attackers from seeing me.
If you have a false positive that is also very concerning and should be dealt with. At the very least I can put a piece of tape over the camera after the light turns on, if I believe it's a false positive.