This can be a difficult topic for many people to reply to (myself included) because a full answer from them would bring religion into it; however, I do want to respond to two points from Goldomark and Zombie_Babies:
No I'm talking about ending the hypocrisy that leads to affairs existing. We should stop glorifying something that a lot of people can't perform (fidelity). There would be a lot less strife if we just accepted that some people need to fool around or have multple partners.
These are my thoughts on the subject, to answer BG's question.
My opinion is that if marriage were as easy as breathing or coitus, we wouldn't even be having this discussion right now - the commitment of marriage IS difficult! It's why we glorify it. We also glorify firefighters and policemen in western society, because not everyone can rise to those callings and perform them day in and day out. It's why we celebrate achievers in different fields -- they are uncommon individuals, and seeing a Buffet, or Einstein, or Jordan or Baryshnikov is an example of diligence and dedication that one can aspire to. To not celebrate something BECAUSE not a lot of people can perform that level of commitment misses the point of recognizing the commitment itself.
Yeah, that makes a lot of sense: break one moral 'law' and you'll break more. Let's apply that to something else, then: A man who jaywalks is a man who will slit your throat. Break one law and you'll break another - no matter how unrelated - right? Silly. It's just silly.
The problem is that your solution in no way differentiates between the two.
In my opinion it does -- your counter of Jaywalking vs. Homicide would be equating two different types of behavior, negligence to homicide, but the original quote compares one example of trustworthiness to another, lesser, example of trustworthiness (Marital Fidelity vs. Professional Fidelity). A better comparison would be Jaywalking to Running Stoplights, or intentional homicide to -- well, very little, really, western law puts it into a class by itself. In my opinion, yes, a person who cannot keep a vow to a spouse, is more likely to be unable to keep their word to a mere business partner. Not to say I wouldn't go into business with them, I'd just force 'em to sign one heck of a punitive business contract.
Note most people who are outspoken here are also making a distinction between the mainstream definition of "An affair" versus an open marriage, or polyamorous relationship -- one in which all parties are aware of one another and their intentions toward one another. The subject of polyamory itself is a separate -- and even more loaded -- topic, of which I can say if it works for that unit, then great! It's just one where in my firsthand knowledge has never seemed to work out very well long-term for the people involved.
My wife and I have been married for over 20 years, have never cheated on one another, never had the desire to, and barring any catastrophes I see myself growing old with her and only her. Fortunately, we also grew up in the same local community, and share similar values, so it's never been a source of conflict either. Is marriage hard? It's been damned hard at times, whether it be about money, or family tragedy, or lack of communication with one another -- but I also deem it worth it to have worked through any trouble that came our way, and the incredibly strong bond that we share, almost to being able to anticipate each other's needs without thinking. To be blessed and dedicated enough to have that bond with another person, hopefully for the rest of a lifetime, is something I deeply treasure.