Yeah, I don't understand what they're getting out of it. Here's my pros/cons list:
Pros:
trust?
Cons:
if you break up, they can screw you
if there's a data breach, you can get screwed
they accidentally leave their phone unlocked
send phone for repair and the tech sees the video
they accidentally send it to someone else, mistaking it for another
That doesn't seem very balanced to me... Instead of mutually assured destruction (assuming this is reciprocated), just be a good BF/GF? Why isn't that enough?
I think it's honestly just a test and the person does actually believe those things but is saying it as a "joke" to see how far they can push it with their new partner. So the biggest pro would be "did I find someone equally as racist and shitty as me and if so, score", I guess?