Every cartoon has music...AND you had no idea what it was when you were originally watching it. Kind of an invalid argument.
The argument is perfectly valid, for me at least. I realize I am admitting my total geekness here, and flame away if you must, but I read Hamilton's Mythology (the college text) when I was 8, could tell you all about the Greco Roman and Norse gods and goddesses, and preferred classical music to regular radio until around 9th grade. So yeah, maybe not when I was actually 4, but by the time I was in middle school I loved the cartoon music so much that I borrowed the vinyl from the library. Looney Tunes was one of the few to use actual, well known classical music pieces as opposed to a musical score written for that actual cartoon.
To me, something is still educational if it inspires a child to want to find out more about a topic. I loved Rabbit of Seville so much, I wanted to hear the original work. If my son wants to find out more about dinosaurs because he saw a dinosaur cartoon, then that's a good thing.
I let the kids watch all the Looney tunes they want, and then in the car on the way to school, I play some of the classical pieces they have heard. My 4 year old asks for "the cannon song" (1812 Overture) and the "Run really Fast Song" ("the Toreadors" from Carmen) and the "dancing lady song (The Can Can from Orpheus) and "the bumblebee song".