E.A.
I had a colicky baby, 4 actually. I can't imagine leaving them to cry alone through that. We carried, strolled, bounced, showered...but never would I leave a crying baby alone. A sleeping baby in a safe place? Yes, but not a crying one, unless my nerves were so fried I had to walk away for a couple of minutes, but not longer than that, and only for my own sanity because I often did bedtime alone.
I had a friend who had two babies who would fall asleep by having their backs rubbed for a minute or two. Not mine. I agree most with Mom2Many's post. No grey area here for me, either, we threw out the crib and got a king sized bed when the first one was 4 months old and never looked back. We co-slept with them until they were about 3yo. None of my kids were damaged by it, and we all slept better for it. Do I think it's for everyone? Nope, but you'll never convince me that trying to train a baby by leaving them alone to cry is ok, ever. jmnsho.