Are you advocating illegally assaulting people for merely words?

Not assaulted but they will face repercussions. The expression is a common one for American native English speakers.

https://en.wiktionary.org/wiki/snitches_get_stitches

This expression comes from the getto's of America and it means anyone who tells the police anything will get hurt badly or their family hurt or killed.

Anyone who airs dirty laundry is called a gossip not a snitch.

It literally means that people that tell, even if they report a rape or something truly disgusting, will get stitches (beat to the point of needing stitches) for telling on someone else.

in a way, he's saying snitches deserve to have their wounds properly sewn up.

in countries with free healthcare, everyone gets stitches when they need them, not only snitches..