You’re totally off the mark with your moral theology in the STD-infected husband hypothetical story. The morally correct response to the desire to perform coitus in that situation would be abstinence. Any act of intercourse that introduces an artificial barrier to the possibility of conception is a denial of the authenticity of the conjugal vows. Period. The (morally correct) desire to not infect the wife is satisfied by abstinence. The desire to express the meaning of the marriage vows is satisfied by a thing called chastity. Chastity, when properly defined, means expressing love in as many ways as possible. In this case the ways possible does not include intercourse. The presence of sex in a marriage is vital, but without a cultivated chastity it is problematic. In situations like this the desire to have sex has more to do with satisfying an attachment to the pleasure rather than expressing the true meaning of marital love–which frequently involves the Cross and a lot of self-denial.
The only edge-case for the moral use of the prophylactic that I’ve encountered is in regards to semen analysis (e.g.) to determine whether a man is infertile in couples who experience difficulty in conceiving a child. In this example, the condom is perforated and the couple proceeds with intercourse in the normal manner. (Good luck making it seem “normal”!) The possibility of conception is not negated, nor is the integrity of the marital vows.