Yeah, I guess in retrospect the fear is ridiculous. I'm realizing that I am or can easily become pretty kinky, but I don't have and am unlikely to develop any true fetishes (i.e. can't have a satisfactory sexual experience without them).
The other fears are similarly unlikely to be realized. The most likely would be that I would sexualize enemas to where I might get an erection should I ever have to have one in a medical setting. Well, I like anal play and genital play and have had doctors poking around at both my ass and cock without much resulting tumescence, so I'd imagine the same would go for a enema administered in a medical setting.
As for the "child's horror story" of "you'll get hooked on them, your wife will leave you, and you'll wind up a dirty old man masturbating on the toilet with a hose up your ass and bowels that will never work right again"... well, that's as ridiculous as it sounds.
So, yeah, I guess I might try baby steps. As I've noted before, I'm taking enemas anyway, so I might as well enjoy them as much as possible. Start with focusing on the feelings of the enema, maybe move on to fantasizing that it's my wife's hands caressing my bottom, preparing my anus, inserting the nozzle, and giving me the enema. Then maybe, who knows, some day it will be her. I've already found out she's a bit kinkier than I thought when we married.