What do you mean we shouldn't have a first and last name input?

explains the naming conventions of every culture on the planet

Which is not relevant unless you are trying to support every culture on the planet. Which most people aren't, and for them it'll be just fine to have first+last name.

You'd be surprised how often two fields mess up names if you live in a place that has any amount of immigration.

Agreed! My team is constantly humbled by the mess of user data: names, birthdays, addresses, people dying or living abroad etc.

Honestly, sometimes I think about the linear algebra, AI, or robotics I learned in school and get this feeling of, "Is this what I'm doing? Stuff that feels like it should be simple?"

It's funny, even our product manager - who is a great guy - can fall into that "come on, this should be easy" mode, and I'll admit I sometimes get lulled into it too. But to his credit, every time I walk him through the actual edge cases, he totally gets it and admits it's easy to forget the on-the-ground complexity when you're in 'planning mode'.

So yeah, seeing your comment is incredibly validating.

Just validate the registration form? Surely this is a solved problem?

Uhhh...