There are probably several, simple and intricate reasons why I am a fan of The Smashing Pumpkins. To name a few:

1) They [bad word removed]ing ROCK (Vague, I know-but I like this reason)!
2) They're not a superficial band-Over the years, they've really focused on making great music-Nothing more, and nothing less.
3) There's a certain purity in their music, as well as Billy's song writing.
4) Siamese Dream and Mellon Collie and the Infinite Sadness. That, pretty much speaks for itself.
5) Their uncaring drive for this constant, and unique center inside the great, and sometimes truly scary, world of music in the United States, today.
6) As people, they seem like people I would want to be friends with. They seem like really great people. Yes, even James and D'arcy(:
7) They have this great rags-to-riches story. Well, maybe it didn't come from rags, per say-but it seemed pretty dang close to me.

Final note (Added from Reason #7): Check this out, everyone-
http://www.thepumpkins.net/content/view/191/85/

[or]

http://youtube.com/watch?v=rsu41TWEOAE
(This is the same documentary, only it's divided up into six parts).