I have my own studio and do not see a problem with them in that setting. Our clients are always with a trainer, and dumbbells are handed over and taken back to the rack.
I personally own a pair and use them for any exercise I want to do, even though I prefer to be barefoot it I possble can.
In a regular gym setting, though, I can see why they make the wearer very vulnerable to the negligence of others. A regular pair of sneakers protects the feet much better from injury.