It's hard to condense the many complexities, eccentricities, and contradictions into one message. I suppose for me the overriding theme is the acceptance and defiance of the outsider. I think it's really a very personal thing for Morrissey. As if he's taken all his neuroses/weaknesses and turned them into strength/vitality. Somehow his vision has managed to encompass many areas of human life, and his ability to dwell on people's bleakest experiences with a weary resignation somehow inexplicably resonates in quite a positive way within our lives, I think. I suppose its ultimately the old alchemy of turning darkness into something of beauty.
What's the use of "a general overriding message"? No body of writing worth paying attention to has ever had a " general overriding message". Ever. Morrissey's is no exception. I mean, what'd be the point in something that can be summed up in two sentences? You can sum up a f***ing soap product in two sentences, things of actual value are more complicated. I'd rather recommend spending the rest of your life pleasurably trying to discover the endless layers of meaning that Morrissey's lyrics, much like other great literature, contains. If you want general overriding messages, listen to Paul Weller.
There are many facets to Morrissey's work but to me the overarching message is that of the self. By this I mean that we are what we are, and Morrissey most certainly is what Morrissey is! A combination of many factors including both natural and inherited traits and external influences merge to form us as individuals. It is my opinion that a lack of individuality is one of the greatest threats posed to our society. By accepting 'we are what we are', however different we may be to others, we allow our individulaity to blossom. I see individuality in all of Morrisey's lyrics, with a marked uncomfortable relation to the self in earlier work mellowing to a more accepting position as his career has progressed.