Namely, by NOT commenting on or re-sharing content like this horrific video of several young men torturing a kitten to death. Nor posts that include parts of this video or put the content in a different context.
As hard as it is, any form of interaction only helps "free riders" gain more reach and, as in this case, leads to ill-considered rants.
You can only make a difference by "reporting" properly.
We have created a fact sheet that will help you react correctly when you encounter content like this.

www.zueritoday.ch/tierquaelerei-auf-social

www.susyutzinger.ch/SUST%20Merkblatt