I remember reading a comment a while ago (on Reddit, ironically) which pointed out that SFW subreddits naming themselves [subject]porn are borrowing the wrong part from the word "pornography". "Porn" is from greek pornē meaning "prostitute", but the suffix -graphy means "to write" and is often used to indicate "the study of" the thing it's attached to (e.g. geography, cryptography, demography, etc.)
It would be more accurate, and perhaps less controversial, if these communities named themselves earthography, spaceography, unixograpy, etc. As an added bonus, the -grapy suffix is also prominent in "photography" which is appropriate considering that many of these communities are places where people share photos of the subject matter.
I think you're missing the point of the -porn suffix. Its not supposed to convey "the study of" or "images of". Its meant to convey that viewing it is satisfying in some primitive/emotional/aesthetic way. NaturePorn isn't just "pictures of nature", it's "pictures of nature that suck me in and make me want to see more". In that regard, the comparison to sex is intentional.
Literally anything else. Earthpics, coolearthpics, globescope, naturerama, third planet...that was just 5 seconds of thinking. Using the word porn for everything just lacks creativity.
Is there something about the word "porn" that actually communicates "really pretty pictures of something but without any human creations" beyond its Reddit meme usage? Because it doesn't for most people.
Also, not all community rules and objectives need to be in the name and URL. The word "porn" in URLs is problematic for users sitting behind state or corporate internet connection though. Be kind to your local network administrators!
Porn in the sense of something that is the sort of over the top example of a thing that elicits an almost aroused response. Like a gratuitous picture of food would be considered FoodPorn. Or like 2 perfectly machined pieces of metal fitting together perfectly would be EngineeringPorn.