There may not be a "written" rule saying when and when not to go for two. But there is an unwritten rule called "class" and another called "respect" and yet another called "integrity" that pretty much says not to rub the other team's nose in sh!t. To me, KF is the gold standard in class, respect for his opponent, and integrity, and if he wouldn't do it, then that tells me it's just flat-out wrong.
KF has class. He acts like a classy himan being everywhere. Sometimes on the field it is almost to a fault, but if that is his biggest fault, then he has lead a pretty upstanding life.