How do I convince someone that Open Individualism is false?
I don't know if this is exactly what you're looking for, but the only way I've found to make philosophy of identity meaningful is to interpret it as about values. In this reading questions of personal identity are what you do/should value as "yourself".
Clearly you-in-this-moment is yourself. Do you value you-in-ten-minutes the same as yourself-now? ten years? simulations?, etc. Then Open Individualism (based on my cursory googling) would say we should value everyone (at all times?) identically as ourselves. Then it's clearly descriptively false, and, at least to me, seems highly unlikely to be any sort of "true values", so it's false.
This is a thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. The previous "stupid" questions thread went to over 800 comments in two and a half weeks, so I think it's time for a new one.