Well, this blog is in FAVOUR of Batman. Yes, Batman has the potential to be a realistic, noir, people's hero. But, here's an excerpt from grant Morrison's "Supergods", a review and historical explanation of superheroes throughout history. (so yes, this is not a blog of my own, but an excerpt of what someone else had said)

"..decade's worth of unfiltered madness as DC writers used every trick in the book to keep Batman away from the crime-haunted streets where he belonged"

Oh look i decided to provide you with pictures instead of writing it out. Then it's done. This is why Batman should stay away from aliens, and does not necessarily belong with a JLA. People WANT to see him in a JLA, and if aliens DID attack Earth, he would be a valuable asset, in strategy and equipment departments at least. Superman fighting aliens is equally dumb, but at least he has cosmic heritage. This chapter (titled "Superman on the Couch") also has a lot to say about how dumb and retarded Superman stories from the Silver Age were. Ideally I'd say the component of Aliens should be kept at bay unless relevant. the Swarm, the Skrulls and Kree are kind of different, in that they also portray the attitudes of European countries in the Age of Exploration.

But Batman works best at "where he belongs", in Gotham, fighting on the street level. Yeah he does. And it's a great story when he does.