Daf Yomi - Chagigah 23

The Daf discussed Chazal's occasional tendency to enact a decree in reaction to specific mess-ups. 

 

What is the purpose of enacting such rules?  Let's take the Parah Adumah incident.  There was once a man who took a vial of Parah Juice on a boat across the Jordan river.  A human bone was found on the boat, and the vial was rendered Tamei.  The Rabbis reacted by either decreeing that Parah Adumah ashes or water may not be transported over a body of water unless it's on a bridge, with feet firmly planted on the ground.  According to R. Chananyah ben Akavya, the decree only forbade transporting the ashes on a boat, on the Jordan river, exactly like the incident that motivated the decree.

 

How does such a decree prevent future occurrences?  How would R. Chananyah see any deterrent power in his version of the decree ?  

 

It seems that the "why" is overlooked.  I know it is not common to ask those kinds of questions when analyzing a sugya.  And when we were learning the daf, I did not really pause to look into it.  But as I mentioned with regard to the Chaver vs. Am Haaretz sugya, it's something that merits further study, even if not in the conventional Yeshivish style.  Perhaps it's a question for academic Talmud scholars to delve into.  But it does fascinate me, and I shall chalk it up as another perplexing gemara.