A focal plane shutter can be as quiet, listen to a Leica. Just takes some engineering to do but b/c the majority of cameras were slrs there was little incentive to design a quiter focal plane sutter.

I do have a preference for leaf shutter cameras and one reason I like the Contraflex and Contrarex oldies even for slrs when it comes to 35mm slr systems even though you have to wind the advance to reset the mirror which I always found a good thing as it reminded me to wind the film and not have a surprises when I pushed the shutter release.