> Second, to complete the registration process, I have to either supply a debit/credit card, the will call a phone number and somehow compare that against phone records to verify my identity, or send me a postcard.

This is actually a HUGE piece of what makes the social network special. This builds inherent trust into the network so you actually know that the people that you're talking to are actually who they say they are and actually live in your neighborhood.

This means that, if you're selling your couch, or buying something from a neighbor, you can be sure that it's trusted neighbor that you're interacting with.

This actually HELPS privacy rather than impeding it.

Nextdoor also cross references with sex offender databases as well as "some" criminal databases so that they are banned from joining. It's also a safety feature.