I'm sure there's a criminal underworld where you can just buy a passport to get you into a country, but for the average person, passports are really hard to fake, which makes them good enough as identity for logging into your average dog photo sharing site.
Why would I want to log in to a dog sharing website using my real identity? Maybe I'm an outlier but I really value the pseudonymity possible thanks to the internet. I can share as much or as little about me as I want, and the dumb things I probably wrote when I was 14 are not immortalized with my name next to them.
