I'm not a big fan of these classes, but I don't think they should be "banned".
First off, my perspective is primarily one of a cold water diver. For our conditions I don't think these classes give you enough context to be able to dive competently ... even at an entry level. Most certification agencies really put the emphasis of their classroom material around warm-water diving conditions (since that's what most folks do), and leave it up to the instructor to provide the context for other kinds of conditions (i.e. low vis, cold water exposure protection, etc). From my perspective, the vast majority of folks who go through these week-end special classes do so because they just want to breathe underwater and really don't care to know anything else. It isn't important to them whether they have to walk on the bottom to move around, or whatever, because all they ever really intend to do is go on a vacation someplace tropical and follow a divemaster around and do whatever they're told to do. For those folks, even a longer class wouldn't help all that much because learning to be a good diver isn't their priority, and very few of them would get much more out of the class anyway.
Those divers who are interested in becoming good divers will seek out the knowledge they require one way or another ... usually with follow-on classes and by seeking out dive buddies they can learn from. That's my experience anyway, having mentored dozens such divers coming right out of OW class.
There is a definite difference in the type of divers that come out of the full-on OW class, as opposed to the week-end wonder class ... but that may be due in large part to the fact that there's a definite difference in the type of person who'd seek out each in the first place.
My opinion ... people will buy what they want to buy. Diving's a self-regulated industry, and with a pretty good safety record overall (statistically). For the most part, we're all adults and can decide for ourselves how much training we want or need to pursue this hobby. I'd like to keep it that way ...
... Bob (Grateful Diver)