>Strictly speaking: yes, porn is against the rules.
To clarify, this is only because "NSFW" is explicitly forbidden by Rule #2 and "NSFW" includes pornography in virtually all cases. The problem is that nobody really bothers to sit down and explicitly outline what counts as pornography, which isn't actually that difficult, I'd argue. This is why I'd simply strike the "NSFW" part out of the rule and instead explicitly define pornography.