Here's an interesting article from authors with a couple of views on the use of condoms in fiction. And another about fictional condoms, particularly in m/m fiction.
My personal view is that fiction is not really subject to rules, and that each fictional situation is different in any case. I'm uneasy about fiction that preaches, yet I'm also uneasy about fiction that wilfully and without question propogates risky and perhaps very subtle subtexts, such as 'we may pretend condoms are okay, but really everyone knows the BEST sex is only bareback'.
Sometimes I get the impression people are trying to push those old, tired arguments about condoms spoiling sensation or being a passion-killer with the angle that 'fantasy' sex should be condom free. It's the presumption that condoms are unsexy that I'd question.
Basically, I think there are no 'shoulds' in fiction.