I think the poster's point is that people are reducing themselves to 0 or 1. That's essentially the problem with identity politics, people are complicated with many facets; why would you latch on to 1 identifying trait?
What a person's specific religion is isn't interesting, just like their hobbies aren't interesting. They just don't say a lot about the person.
What _might_ be interesting, is if you only have one interest in life. e.g. Bubba Blue (from Forrest Gump) isn't someone I'd want to spend a lot of time with, even though I like shrimp.