There is no debate. Playing with multiple weapons that must be learned how to counteract each other, or playing with one weapon I can spam all day long and never run out of ammo (and get ikills in the prodcess.) I wonder.
I think Insta players play it cause they can actually get frags that way. I remember I was playing Insta once in UT99 and I had mastered the top tactic of it (aka spam everywhere.) I fragged Rev._Whoopass. I never would have killed him with normal weapons. But hey, since even a shaved gorilla could kill the guy with a thousand frags on the board, I guess I can see how people might play it. "Oh look, now I can get kills! YAY!"