60-80% of communication is none verbal.
That's a figure that gets thrown around a lot, but I've never seen a decent source for it. Personally, I think it depends on context. E.g. suppose that you watched an episode of Eastenders on mute. I agree that you could probably follow most of the plot, e.g. "those two were kissing but now her boyfriend's found out and he's not happy about it".
On the other hand, suppose that someone filmed a daily Scrum meeting. I've never attended one, but as I understand it each person will stand up in turn and say 3 things:
1. What I achieved yesterday.
2. What I intend to achieve today.
3. Any obstacles.
Do you really think that you'd get 60-80% of the information by watching that video on mute?
I had a similar conversation with a trainer a few years ago, and they suggested that "not every 10% is equal", but I didn't find that very convincing!
If you're in my team and it's my meeting then cameras are mandatory unless there is a reason that day that you can't put it on. No camera, I kick you out the meeting. If you can't participate in meetings then you can't do your role and you'll be released.
I won't have anyone, however good they think they are, being an @rse on my team ... just plain bad manners mate.
You're welcome to set that policy, but it feels a bit draconian. I don't mind using my camera, it's just a bit of a faff. It's built into the laptop lid, and I normally have my laptop closed (connected to external monitors); when I open the laptop, that will block part of the monitor behind it, so I wind up peering over the top. Also, I'll need to close my curtains and turn on the lights, otherwise the daylight from the window will give too much glare.
More generally, think of other scenarios where people don't use video. Online gaming is a good example: everyone's looking at their own screen, so they'll talk via headsets but they don't need to see each other faces; they'll just yell out "I need healing" or whatever. A work equivalent is when someone does a screenshare to go through an Excel file (e.g. the risk register). If everyone has that full screen then it won't matter whether other people have cameras on or not (because you won't see them); even if you do split the screen, you'll be squinting at tiny faces.
Another scenario is an old-school phone call. If I'm on the phone, that gives me the flexibility to stand up and walk around, rather than sitting still the whole time. Is it bad manners not to turn on video for every phone call?