Your not wrong about that. At least ours in the 2013 Chrysler does not have any defrost capability. But you can always brush off snow before you get into the vehicle. The camera is somewhat protected as it has some overhang, and points generally down. BUT the type of snow you are speaking of would likely cover it.
The same people who don't completely brush snow off their windows up here, probably wouldn't bother with the camera either

.
I'm not anti-camera per se, just don't want to see another area where people (dangerously) assume blind-faith in yet another tech crutch. Even for someone who pays attention to operating their vehicle, if you take a long drive in the winter time, under certain conditions, it is easy to pile up snow on the back of the vehicle. For that matter, snow and ice on the front too. LED lights on the rear add to the problem, as their lack of heat limits snow-melt.
In a public space, I prefer to back-in, or drive-thru. With modern vehicle design, there will be times in Winter up here where a camera may not show me anything.
I was
really impressed with one camera setup I used briefly. I used to shuttle RVs for a buddy who owned a service shop. He had finished working on a 32' class C that was nosed in against the building. He asked me to back it out and take it for a spin. He had a big yard on the front of that shop, with 2 entrances - people tended to pull off the road at relatively high speed. The owners of that 32' had installed a high-end camera on the back - great dash screen, but also are really good high rez wide-angle lens on the camera. With the camera mounted up high on the RV, I could clearly see the
entire big yard,
both entrances,
and a decent portion of the road. Stock Ford truck mirrors on those chassis are good, but with zero visibility on the back of an RV, I really appreciated the performance of that camera.
When I have to back up in a public space, I often throw the 4ways on, and slowly back in. As careful as I try to be, what does scare me is how totally oblivious many people are (even around a large vehicle) when walking, esp. with a screen in their face.
Rgds, D.