Nice post Robin. Certainly I agree with Wesley that 'thou doth protest too much' but hey a little ranting on the subject was just spice for the many good points you bring up.
The central idea I extracted from your post was that one should just enjoy (or not) a film without adding sacredness to it some some label. In other words, that somehow the label elevates the movie to something we SHOULD like because it is 'good'. Balderdash. I agree with you, the thing is either enjoyable or not. Movie theaters are not churches! Film study nerds are not one iota holier than computer nerds. One watches movies, the other plays with computers, no holiness conferred by either.
Yet, as you say, humans like to classify. It serves purposes. I've just started watching Noirs as a study. It helps to have the classification if only to get a list of 'similar' movies and to have a point of comparison. It is also fun to recognize some of the techniques and methods of the Noir in other genre. Sometimes such things carry a underlying story line. Little signals from the director, 'inside' jokes in a way. In the past I've missed quite a lot by not recognizing patterns from the past.
I agree that Film Noir does not deserve it's own genre just because it presents a pretty dour, pessimistic, and dark view of life. However, its technical tricks of camera angle, dark and light, settings, characterization, and so on do add up. There IS pattern to it. You know, if it walks like a duck, acts like a duck, and quacks it's probably a duck and not a platypus, but hmm maybe... do platypi quack? I don't know. But I do know this, I have heard your warning and I promise I will not let the fancy classification scheme sway me when it comes to deciding whether I liked the movie or not. That call doesn't belong to anyone but me. I don't care if it quacks, if its only a platypus so be it.