My take, when it comes to the line between good bots and spambots, is that bots should not interact with users unprompted.
A bot which mentions users, misuses hashtags or is not properly marked as such via NIP-24 should be considered a spambot. A bot which is marked as such and only replies to users if prompted to do so, in order to offer some kind of service, should be regarded as a good bot.
As for pornography, my take is that it should be allowed except when it's illegal or spam. It's just like any other kind of content one may disagree with. Requiring that it be marked as sensitive via NIP-36
can make sense.
(Of course, your relay, your rules, this are just my suggestions on the topic).