I can't imagine that anyone worldwide was going to buy their first and only smartphone, but decided to spend more to get a special high-security black phone, and is then without a phone because of this. And even if they were, I'd rate the safety of even one user who'd accidentally click through the warnings and make a call that should have been secure but wasn't, as paramount.
If my smoke/heat/etc detector starts to fails I don't want it silently dropping back to a smoke-only detector. I want it to start beeping loudly and refuse to stop.
> If the user is informed they have a non genuine device that is not safe or secure
Having to flash a new OS onto it is an appropriately sized clickthrough for a warning of that magnitude. Like being woken in the night to change a smoke-detector battery.