Yeah, sometimes I find myself looking at it from two angles at once. On a linguistics level, semantic change is interesting -- extremely so -- and one records and analyzes the full range of usage without prescribing which directions of change are "good" and which are "bad".

Then there's the personal level. I mean, it is true to say that using "gay" to mean "bad" is a case of specific-to-general semantic drift, but it is also true to say that it hurts people's feelings. And that's the point where I find it quite justifiable to take off the linguist hat and start prescribing usage all over the place. :P

Clearly our spoons and your knives are running away together.