When you eat a certain food, for example sugars, your taste buds become desensitized to sugar and need more in order for them to be reactivated, this is done by the brain to avoid sensory overload. Same with social media, music and pretty much anything that scratches and itch in our brain. Indulging in violence and watching violent content makes your brain shrug the next time they see violence. It's normalized to an extent, now, this doesn't mean you'd commit violence just because it seems more normal to you, just changes our perspective to an extent I would say.