I didn't say they were unable to grasp violence, I said that they were unable to grasp the reason behind it (ie. standing up for something) and therefore would likely be unable to grasp the other sensitive topics that people are bringing up from Sesame Street. Kids grasp, and usually enjoy watching, violence in movies. They don't usually grasp the deeper message being sent by having it as a part of the show.
As to Hasbro putting it into the show, I don't think they need to. They teach plenty of worthwhile lessons centered around the ideal the show was built around, "Friendship".