Eh, I don’t think it’s be a big deal. Slap a giant warning on it, all good. Super common on all sorts of platforms. Anyone trying to claim their encryption doesn’t work because they have a (scarily labelled) option to disable it can be easily demonstrated to be disingenuous.

And worst case if someone does disable it but doesn’t implement their own then their email I just falls back to… the same as any other platform.

They might not want to take the time to build it, but I think what this dude is asking for is a totally reasonable thing.