No, the idea is to suppress it to a level that is acceptable to fire without hearing protection (e.g Hunting) without going deaf for three days and suffering permanent hearing loss, i talk from experiacne trust me. Sub-sonic rounds, although something cool to play with, would make it less effective than a 9mm subsonic Ball round which is bad news for a hunter.
I'd like to add at this point that i see outlawing suppressors is like outlawing sunglasses beause a criminal MIGHT use it to conceal his identity and escape from a crime un-punished. Shooters and especially hunters that tend to fire off multiple shots in one hunt where ear protection can't practically be worn NEED them to prevent hearing loss.
Edit: They also reduce recoil like any muzzle break would which would prevent broken bones like colar bones and noses.....once again i speak from experience

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