In my opinion the brutality that goes on has nothing to do with being 'Mexican'. Given the same circumstances any country could become another Mexico. Colombia, Sicily, Yugoslavia or the Soviet states were once just as bad. It just wasn't documented as extensively.
Even when you go back to the period of the American Civil War there was gruesome stuff going on in the scalp-hunting business of the White Southerners, Native Americans and African Americans, which in it's purest form was also some sort of organized crime.