Generally speaking, though, dealing with things on a case-by-case basis is the appropriate and intelligent process. You're perfectly capable of analyzing a visitor's swastika tattoo within its own context, and determine whether that particular individual is, in fact, someone you're willing to allow into your house, without having to apply a hard-and-fast a priori rule.

Unfortunately, as the Reddit post describes, dealing with case-by-case analysis of pornographic material posted to reddit was simply consuming too much time and attention from the admins. They could either scale up their staff for dealing with grey-area cases, at the expense of other activities they might undertake to improve the site, or they could simply no longer permit grey-area material outside a certain boundary to be posted on the site. They chose to do the latter.