I don't buy your 'safety' argument at all. Any system that forces you to perform an action before moving a foot off the pedal is going to be less safe when your bike starts to slip out from under you on a patch of black ice. How many people do snowy winter commutes with clipless pedals?
I would agree with you, for riding on ice or snow.
That's a very specific situation though. How many people do snowy winter commutes in the first place?
My feet do not slip off of flat studded pedals, they're stuck on like glue. Due to that claims that clipless are safer for slippage reasons while commuting just seems kinda silly to me.
Maybe you have been lucky so far, or maybe you have very smooth streets to ride on and never curb hop. I've had it happen, including with studded pedals. It only takes one time of accidentally hitting your shin with the studs to decide they aren't so great afterall.
If your feet are "glued" to flat pedals, that means you must be pushing down on them at all times, which means your other leg is also having to push up against it. That's where the efficiency difference comes from. If you lift up on flat pedals in order to avoid one leg having to lift the other, your feet would slip.
If you want to really feel/understand the difference for your self, take one foot completely off the pedal, and try riding with only one foot. Doing it with flat pedals is impossible. Doing it with cages or clipless is easy (and improves your pedal stroke if you practice it often!)
I'm not entirely sure that I buy your 'control' argument either. You control the bike differently with clipless than with flats . . . I wouldn't say it's a clear cut better or worse.
Try doing some serious single track mountain biking and/or full on urban assault style road riding (curb-hopping, speed-bump jumping, track-standing, yellow-light sprinting, confused-pedestrian and careless driver avoiding, all at top speed) with both type of pedal and then say if there is a clear-cut better or worse.
Now, maybe most people have no desire to ride that way, ever.
Personally, that's just how I ride. Even for a 1 mile trip to the store. Maybe my bike messenger past. Then again, I think I always rode that way, and it's why the job appealed to me...
I'd be interested in seeing a study showing the improvement in efficiency between clipless and flats . . . it makes sense that they would be a more efficient since you can completely deweight a foot while pedalling at high cadence, I've yet to see a study that shows there's a tremendous difference between flats and clipless.
http://www.sciencedirect.com/science/article/pii/S0765159799800550 (scroll to the bottom for Engilsh)
http://www.ncbi.nlm.nih.gov/pubmed/20827654Don't get me wrong, I'm not saying its that big a deal to not use them.
I have flats on my folding bike, and its what I ride most these days. If you don't put in much mileage, its probably not worth the money.
I'm just pointing out that the criticisms presented here don't necessarily hold up.