http://www.youtube.com/watch?v=FKfMqwSMI4U (I just had to link this :-)
These men do not "respect" the institution of marriage or the religious views on adultery etc.
There are entire forums on the internet devoted to "how to get a girl in a relationship" with "boyfriend destroyer routines" or whatever.
The idea is that an institution employing experts with lots of experience in poaching employees, is going to have an unequal advantage over the employee, and is likely to entice them either through souring their relationship with their current employer (maybe telling an employee about how Apple's workers are treated in China, for example) as well as using psychological tricks to lure them away.
Flirting is one thing. Blatantly propositioning in front of the husband when he's ware of it is something else. Most people draw a line not because they want to flaunt some antitrust law, but because of biological / economic emergent actions.