When I was 13 I hacked my right index finger open to the bone with a pair of scissors by accident. Pretty sure THAT is probably what desensitized me totally from in-game blood, sometimes gore... since in comparison to looking through rice-like body tissue (that's pumping out red ooze all over the desk whilst a class of people scream and I feel like I'm going to faint) to the very structure that holds my insides together, it's REALLY quite tame. Though ever since, the realistic sight of blood & deep or horrific injuries, or sometimes even just the implication, makes me sick to my stomach... hence why I very infrequently watch horror movies.
I guess where I'm coming from is that at such a young age I was more than capable of differentiating virtual reality violence in a fantasy world or scenario, and real-life human suffering or realistic depictions of it... and nothing's changed in 5 years, if anything I'm more aware and sensitive to it. I'll happily slaughter an army of pixelated peons in Dynasty Warriors, but the sight of another human in hurt or suffering causes me grief. Probably where my lack of understanding for OP's side of this topic comes from.
EDIT: I'd also like to add that from a very early age I was watching "scary" movies like The Mummy (which at the time was rated AO - advlts Only) and playing games rated higher than my actual age. My parents did draw the line at horrors and shooters, or stuff they hadn't seen themselves or if they weren't around to watch it with me.
And I've grown into a rather passive, sensitive human being. It's not impossible to expose children to violence without them turning into terrors or murderers.
EDIT EDIT:
The laws must be different over there because in the states it is just a rating system that limits the SELLER as to who they can and cannot sell the product to. Has nothing to do with consumption. A warped parent who wants to scar a child can let a 5 yr old watch a M rated horror flick legally in their own home.
It wasn't so much the existence of the laws around ratings and what can be sold to whom, more the sentiment of the rating decision from a government division that I was referencing.
It's the parent's house and power, yes. But the fact that the appropriate division of the establishment that runs the country, who for all I know probably employs or references those experienced in social/psychological studies (I wouldn't know, but I can only imagine) and will naturally have access to consensuses or surveys relating to video games/movies and crime or behavior, has confirmed the product as acceptable for the purchase/consumption of those aged appropriately... doesn't that say something?
Forcing your own ideologies upon your children (depending on what about and their age) when taking this into context seems almost as wrong as doing something like forcing religion upon them. Children need space to experience things for themselves and draw their own conclusions. I'm scared [censored]-less of dogs and I dread going into the CBD. Why? because my parents instilled paranoia within me about both as a child, by making it out like every dog I pat's going to rip my hand off, and every trip to the city will result in me being assaulted - when in reality the chances of both are slim. I do resent them a little about that for going overboard with it.