Two reasons the obelisk is located in St. Peter's square are first to commemorate the triumph of Christianity over paganism (hence the reason for the crucifix on top of the obelisk), and second to memorialize the Christian's (including Peter) who were martyred by the Romans in the circus where the oblelisk was originally located. That anyone would say or insinuate that the obelisk was placed at St. Peters for pagan purposes is just sickening, and that person really needs to re-evaluate their values to ensure they are aligned with Christianity.
Obelisk.....schmobelisk....it is still a pagan symbol. You think by placing another pagan symbol on top of it makes it any better? The Greek word translated cross is "Stauros", namely a stake planted in the ground. This is commonly referred to as a "Tree" [Acts 5:30; Acts 10:39; Acts 13:29].
You folks have managed to pervert that one pretty effectively. You've got the whole world believing that our Saviour was hung upon a Babylonian Tammuz cross. And you wonder why we just chuckle and shake our heads at you.
Good post.
As an aside, there was a fascinating story on A&E (I think) a few months ago that chronicled how the obelisk was moved.