Superman vs. Batman

So I saw the new preview of the new movies Superman vs. Batman. It will be released next year, but they didn't specify a date. It looks like it could be a big flop. What I don't understand is why would they make a movie like this? Why would they have 2 super heroes become enemies? Is there something deeper from the early comic book series where they became enemies? If anything, why wouldn't they make it where they team up against the villains?

I saw an early preview a few months ago....   looks weird, hate Ben Affleck as Batman.   

Yeah I  dunno either, but I am sure it will be good. By the way it's release date is March 25th

The lines are out gentlemen:

I know comics are not reality-based but kind of ridiculous that a mere human (albeit with high tech toys) is fighting against a "guy" who's only weakness is Kryptonite, has laser-beam eyes, can see thru walls, fly at supersonic speed+, not to mention he turn back time for heaven sake in S2, skin is bullet-proof, super-human strength.

This plot point just turn me off.  I'll still watch it as kind of like Snyder.