What a bunch of whiners...
You all suck as GMs, BTW.
It's not about you, it's about everyone having fun. If they want to be Neutral, let them, and make up adventurers based on that.
I mean, with my party who are a mix of neutral and good, I don't go around writing adventures for a party that are a mix of neutral and evil, so why should you, Zerovid.
Plus, before you start whining about how it's "no fun" again, I should point out that I almost exclusively play NG and LG characters, like you, but I know my place, and I know how to have fun without forcing the players to cater to some ill-defined whim of mine that dictates that they must do good.
If your players are just messing with each other, only one person is to blame: YOU, the GM.
How to deal with it? Write adventurers that make them cooperate. It's not difficult. Read up on the prisoner's dilemma, for example. Put them in situations where they lose out by cheating each other. This doesn't force "good", but it means unless they choose group cohesion, they will have a harder time of things.
I've played with all Neutral groups who coordinated perfectly and never tried to screw each other over, who were Neutral because they weren't out to do Good, but to find their fortunes and so on. Morality and Neutrality are not incompatible, indeed, some moralities dictate Neutrality, and if the PCs are simply and genuinely Amoral, they're probably on a quick road to Evil.
So really, "must try harder" is the message. Make situations more complex and require teamwork, make your adventures more interesting and personalities more defined. Make you villians worthy of hate and disgust, not "Sephiroth"-style "Kewl", and maybe the players will actually want to be more involved.
If you can't do this, quit as GM and make someone else run it...