Good point about the IS that I totally forgot in my assessment above. I personally count IS as a negative in any lens. I find its usefulness overrated and see it as another lose part that will shorten the lifespan of the lens. IS -and frankly the AF - will potentially be two of the reasons for me to look elsewhere for a macro lens (and wide angle prime).
Not a very popular view, I know, but one I'm willing to reasonably defend. And just a different perspective. Not trying to convince anyone one way or another.
I agree with you about not necessarily needing AF with a macro lens, but the 100L is pretty useful outside of Macro Photography. I used mine for portraits a good bit when I had it, and got some really fine detail shooting video with it.
I see where you're coming from about IS being a negative, but in the 100's defense it is one of the few Canon lenses with Hybrid IS (part optical and part electronic) and it works incredibly well.