Danke shadow for making points I had not. Sound is OP as fuck, yes which is why we introduced Ototon in a light faction.
Regardless of such, when utilizing an annoying screech like roar; the user projects such frequencies and vibrations with the air itself. Almost like a fuuton/sound wave blast. In my own opinion I feel as if the sounds, ranging off the initial blast are muffled and lowered to a great degree.
Either way saying that the technique should harm the caster, is like saying sprouting a fire ball should burn your skin to ashes. Chakra has a very pixie dust-effect when it comes to techniques and what not. If its the users own chakra is emitting such, more than likely he is trying to harm someone else, not himself. As casters of the sound we can navigate and direct just whom and what will be effected. There are Ototon techniques that aren't even attacks, more so supplementary enhancements on the user. Now contrary, if two Ototon users match up against each other; all hell is breaking loose. You'd probably want to watch from a distance.