I tried that a long time ago and the problem with it was that it produced a lot of false positives for me because I subscribe to a lot of Google Groups.
Can you make a negative condition also, X but not Y?
Of course. But the problem is that the more complicated you make your filtering logic, the harder it becomes to maintain. I was constantly discovering new exceptions to my ever-more-complicated rules, which is why I eventually gave up on that whole approach.