It should be. It is something that is very important. Quite often a woman can forget the importance of it. I feel because she is often thinking about everyone else in the family and their other needs, but sex should be apart of the "vows" so to speak.
I think that if either party is not able or does not want to provide sexually for their partner, then they should be willing to accept professional assistance. In this case, men seeking P4P arrangements via escorts, MPAs, porn/webcam, etc. Whatever happens to work for that person.
I think rules can be put in place to protect the family as a whole. For example, safe practices only, no in your face style tell all about encounters, a budget, no "bringing it home" meaning keep the sex out of the family home and even limiting repeat visits.
I will say that I believe it is important to exhaust all options within the marriage first of course. Quite often a woman will feel unappreciated, unattractive, unwanted sexually etc, Or tired and run down. These are things that can be resolved at times and therefore the sex life will pick back up.
I already admit I am an oddball in my thinking, so I can't really expect this to happen for married couples, therefore I will not judge the married men here for finding their needs met elsewhere.