paminala (I now understand your screen name

), you have a lot of different things going on in your post, so I'll try to address them one by one:
It isn't the gun or the knife or the two by four that kills a person. It is the other person holding it that is responsible.
I will defer to what Leslie just posted.
But the real issue is why that kid picked up a gun and pointed it at another kid, and why nobody said anything even though they knew he was planning it.
I agree, this is the real issue. From what I've read, the shooting appears to be gang-related:
http://www.washingtonpost.com/wp-dyn/content/article/2010/02/08/AR2010020803533.html. As to why no one said anything? If the gang reports are true, I imagine they were either very afraid, or part of the same gang. The larger question here is why kids join gangs in the first place.
Most girls have been hit or abused by a boyfriend before they are out of high school but when Chris Brown beat up Rihanna half of the reporting implied it was her fault. What are we telling them?
Domestic violence is a terrible thing, and has been going on since time immemorial. What is new is our ability to see and hear about it, all the time. And I'd argue that in the past this sort of behavior was kept much quieter than it is now, although of course there are still many women who are afraid to say anything. I'm not exactly sure what your point is, other than that the media rarely delivers news anymore, but has rather become a source of 'infotainment'. It's about getting viewers, not about saying or doing the right thing.
Kids are bullied and pushed around but in which schools do you see anyone teaching conflict resolution? What are the consequences for bad behaviour?
There's a zero-tolerance policy for bullying in our local public schools, and it seems to work. In fact, more and more school districts are adopting various anti-bullying measures. Clearly there's much more that can be done, but it's an issue that is now taken very seriously around the country. Obviously not every school district feels this way, but your question implies that no one is doing anything about these matters, and that's simply not the case.
A high school honor student was beaten to death in Chicago and someone recorded it on their cell phone. That made the news for all of a day before we all went back to worrying about where the next Olympics would be held.
It made the news on various blogs for quite a while, and was discussed at length. I highly recommend
Ta-Nehisi Coates or
The Root.
Girls are catching up to the boys in fighting. Go to your favorite search page and type in "girl fight" then search for video before you tell me I'm wrong.
I don't think you're wrong about the existence of the fights. But you only know about them because the fights are posted on YouTube. For all you know this sort of behavior is happening less now than it did 20 years ago (I have no idea what the actual statistics are, but I hope you see my point.)
As a counterpoint, I grew up in NYC in the 60's and 70's, when the crime rate was sky-high, and heard gunshots (I lived just south of Harlem) on a regular basis. Since that time the incidence of violent crime has dropped dramatically, to levels not seen since the 1950's. In fact many cities in the US are safer now than they were 20 years ago. So while I'm horrified by the fact that a child would shoot another child, I don't see it as something new that has suddenly reared its ugly head. But that may have to do with growing up as a small fish in a very, very big pond.
I have always imagined that paradise will be a kind of library. -- Jorge Luis Borges