If you've heard my rant on Holy Days of Obligation on my Christus Vincit ANYWHERE! (#62), my rant was mild compared to that by Fr. Erik at the Orthometer.
I once heard this justified by the fact that many people just don't go. Can't let the little darlings sin can we? So we remove the obligation. Heck, lets just get rid of the 10 commandment while we are at it, then there wont be any sins at all. (I actually heard of a nun during the felt banner CCD years saying that if the kids weren't taught the commandments, they wouldn't sin.)
YOU GO FATHER!
He's got an excellent post on Christmas, Midnight Mass, and liturgical "double dipping" as well!