If you believe this, you have been watching too many movies. First, let’s call them suppressors, not silencers. The suppress the sound, they do not silence it. A 9mm handgun is usually around 160 decibels (db). Adding a suppressor reduces it to around 120db. For comparative purposes, a lawn mower is around 100db. A car horn is around 110db. Is that silent? Not even close. Widespread use would reduce the amount of hearing damage caused by firearms. It would not turn criminals into silent assassins.
Can you make a gun silent with a suppressor? Kind of. If you take a low powered cartridge like a .22 and shoot it from a rifle with a suppressor at subsonic speeds, you can make it close to silent, but then you have something which is likely only effective at killing rodents at short range.