I feel like reading HN should come with a warning on the tin that "If you're reading a long technical comment, taking away just part of it is dangerous" - were I speaking to someone in the business side of a corp that asked "Hey do we need these FK things, some developers have been saying they're slow" I'd say 'Yes, we absolutely do need FKs' then go on to talk to the developers, double check I wasn't at one of the about dozen of companies with data at a scale that FKs as implemented in RDBMSes (especially postgres, mysql tends to drop off in performance much easier without heavy tweaking) is insufficient, and then tell them that FKs do work and they probably really just need to read up a lot on indexes and stop throwing around table locks like it's christmas.