One objection is the fear, valid or not, of them bending and thus being unable to load the gun.
The bigger issue, for me anyway, is that, thought it's true loading the gun with moon clips is a lot faster than loading individual rounds, the time it takes to load 6 individual rimmed rounds into the cylinder and then eject them is lightening fast compared to the time it takes to load the moon clips and then later demoon the empties.
I have a Redhawk .45 Colt/.45 ACP and a Ruger SP101 9mm. I don't shoot ACP in the Redhawk due to the hassle of moon clips. When I carry the SP101 I carry it with moon clips and reloads in moon clips as well. At the range I don't use them. I prefer the inconvenience of plucking the fired cases from the cylinder one by one to messing with loading and demooning moon clips.
Just a random thought-
If when removing the empties from a moon clip you are "demooning" (often with a demooner tool) why aren't you mooning when loading them?
Just askin'........................................