Interesting debate, to my mind I don't want to actually hurt my horse, just get his attention, and I can do that with a shorter whip with a popper, believe me a hard bat wakes them up.
Personally I would never use force behind the hit with a long schooling whip, it is designed to be a refining tool, used to touch and direct, not as a punishment.
To each their own, I have just found that a crop is ineffective on a lazy horse. I never put all my strength behind my dressage whip unless my horse is ignoring all else. I have had a horse completely ignore a crop no matter what I did with it or how hard I hit her with it, but with a dressage whip, even a tap stings and THAT worked.
Do bear in mind though that the filly I had that ignored a crop altogether is a stubborn extremely dominant witch and even my mother [who owns her now], who has 25 years on me in the experience department and is extremely experienced with lazy horses and gentle ways of perking them up, cannot get this filly to do something she doesn't want to do without a significant amount of demanding.
My system, and Mum's, goes a little like ask, tell, demand, promise, enforce. Depending on how educated the horse is I might skip a step or two but never the ask. My old boy was very lazy, but also very educated, and knew better than to ignore me, so sometimes with him I went straight from ask to enforce [leg aid to hard crack with the dressage whip, on the odd occasion I actually used one, or a hard jab with the spurs]. Never failed to lighten him up for two to three weeks at a time.
I do think it depends a lot on someone's personal experience in the matter. For me, crops are for jumping, and only for use on a horse that's likely to try to stop. I don't even own one anymore, haven't bothered in nearly three years. Short with a popper to make a loud noise, to me, is a warning. There isn't enough bite behind it if you come across a horse that will ignore that warning.