I don't get the Kurt hate. He has both faults and strengths and the show has highlighted both (character wise),pretty much like all the other major characters. And his longest son is actually probably my favorite of the ones he has sung (the one from Sunset Boulevard). But while Kurt does have a a couple scenes, he doesn't sing in this episode. And hell without Kurt we wouldn't have gotten Mike O'Malley my favorite adult character on the show.
Now when the show started the three primary characters were Rachel, Finn and Shue. With each getting major story lines with side characters.
Kurt was the first minor character to connect with fans (student wise) and that really ended up killing most of the adult story lines (those connected solely through Shue).
That really happened about mid way through first season, and continues to this day For whatever reason the fans just didn't respond as well to the adults as to the various students.