Rejecting after accepting

This blog is above all a forum for ethics and morals, so I present the following dilemma (though I suspect this will turn into more of a rant)

Everybody gets very squeamish about discussing going back on job offers. The following rhetoric is commonly used:

1. All HR recruiting personnel talk. News spreads fast. Everybody will know, a la Alexey Veyner.
   
2. It will tarnish your professional reputation - you are screwing yourself early on
   
3. You will end up employed as a Business Analyst
   
4. You will lose your campus recruiting privileges
   
5. You will be black-listed from working there again (or possibly anywhere else in the transitive closure set of HR personnel)
6. It's bad
   

These arguments belong in two groups: heresy and morality. While I can understand the first, I am deeply troubled by the second.
I can accept a vast communication network between HR personnel of various banks. I can accept them cross referencing applicant lists, and I can even accept the possibility of them keeping a distributed listed of applicants in violation of 'unwritten' policy (a black list) as a measure to prevent their companies from recruiting unsavory characters. My two qualms with this are :
1. This would require a level of sophistication not afforded to the HR departments (See next entry)
2. Wouldn't this actually turn into competition favorable for the recruit (me). In simple microeconomic terms, HR personnel having knowledge regarding your other offers would (literally) create more demand than supply. Recognizing that both are inelastic, maybe you'll get a better offer: their deadweight loss is your gain. Also, recruiters can attribute your other offers as certifications of their competency in 'attracting top talent', and have all the more reason to hire you. One can draw a social parallel to this paradigm.

Its really the latter morally based cause that really irks me. The more sapient of my friends have given me the 'you gatta watch for numero uno' and 'there's no love on wall street' advice after some mulling. They do not posses roman numerals in their last names, but I think they possess the necessary mentality to succeed. I'd love to see them turn into macho money grubbing, backstabbing bastards they deserve to be. But I digress. There are two (major) things wrong with applying morality to employment (vis a vis : '6. It's bad'):
1. It won't be appreciated or returned
2. It suggest a slave mentality. Corporate loyalty is the effect of successful internal propaganda. One should not adopt his own personal ethics at work until you have located them in them the 'corporate values' presentations you are subjected to on a daily basis. Until your employer adopts 'morally upright and logical decisions in dealing with personnel' or 'lots of free money for everybody' as a pillar of business principles and a deciding factor in management team strategy sessions, you should not be hasty in applying your Nicomachean ethics.