Is it wrong to only like certain parts of a fetish? Like if someone loved everything about slob except scat and watersports?

It isn’t “wrong” lol. There isn’t really a moral or immoral component here (or rather, if there is, then it’s probably all immoral, and we would be debating degrees, which is never a fun discussion). To me, though, it always confuses me when people refuse to take those last steps. The way I categorize things in my head, if you like slob stuff, it feels almost illogical to not also like watersports and scat in some ways. That said, I know people do feel that way and they aren’t being irrational–they just categorize things differently than I do. It’s a complex business, and navigating it is a bit hard, but I do what I can to please most people.