Why can't the hardware provide access to the raw sensor data and let freedom-respecting software deal with it?

It does. https://patchwork.kernel.org/project/linux-media/patch/0d4dc...

You can think of the VideoCore ISP firmware task as a proprietary application and the Pi Camera as a hardware security dongle for that proprietary application.

You can choose not to run that application and access raw data from CSI if you'd like, but if you want to run the special ISP firmware application, you need the hardware dongle.

I think I feel the same way about the DRMed blob as I do about the Pi in general: I understand why the Pi folks did things the way they did, I don't think it's unethical by any stretch, but the situation is disappointing and I would prefer the alternative.

It does. Most people get enraged about RPI cameras unnecessarily. If you don't want to buy cameras from the RPI foundation and want to use/design/connect your own, nobody is stopping you. If you want raw sensor data off the RPI cameras, nobody is stopping you either. It's only when you want to use their image processing with a clone camera that you run into problems.

I just can't get worked up about this, I think this is completely fair.

This is the same argument for closed-source GPU drivers. "Oh, my special secret sauce algorithms!"

Nah. If you want the cred from being open source, be open source.