It's hard to convey the idea that a real person is behind the faceless snooping, but usually people don't want a real person looking at their private info. "Do you want the cop who pulls your daughter over for forgetting to put the new sticker on her license plate to be able to look up all her beach photos during the stop?"

Cops want to be able to see everything. I don't think it comes necessarily from want to see nude in particular. Government likes power, the more they get, the more they want. That includes cops. They can't think beyond their own mind often. Most people would probably (at the beginning) use backdoors responsibly, but when it becomes mundane they will use it all the time and without compuncture. This leads to power grabs and politicization. If it's not an option at all, it helps a lot.

This. Hence the proliferation of government access to CCTV footage that was originally collected for "serious crime" only.

It'll start out with "we only need to break your e2e encryption for serious crime cases", but in 10 years your local council will be breaking into your dm's to see if you used the right recycling bin.