AZ shooting: why are we surprised?

We live in a society where a mentally unstable person can be rejected from serving in the Army and still go out and buy a gun. This makes no sense to me. Are we living in a country that still refuses to take mental health seriously? There are, of course, other issues surrounding this horrifying incident that trouble me:

1. Ratings-driven cable "news": whatever happened to old-school journalism? Real-life is not that sensational. But the newfangled approach to journalism that sees every-piece-of-news-as-possible-cagefight has turned news programs into pulse-pounding entertainment. I don't mind this, necessarily. But I'm guessing your average psychotic isn't capable of discerning between entertainment news and fact-based reportage.
2. Politicized violent rhetoric: I don't hold Sarah Palin responsible for the AZ shooting, of course, but inciting voters with a "Crosshair's Map" was irresponsible--especially now that one of those "targets" was almost killed. It's sorta silly for a pro-Palin conservative to assert that the map is "no longer relevant now that the election is over." Come on. You don't place bullseye targets over 20 districts, tweet updates like  "don't retreat--instead RELOAD!" and then act all shocked after someone actually follows through (literally) on your suggestions--even if it's AFTER the election. Of course, conservatives aren't the only ones guilty of violent rhetoric. It's just that they have the most popular TV and radio talk-shows so they get the most attention and blame--both positively and negatively. (And I'm a conservative--so this is me being hard on my own peeps, yo). My point is that extra-popular politicians have an extra-big responsibility to behave responsibly. That's it.
3. The effect of our political climate on lone whackos: Conflating the shooter with Sarah Palin is perhaps unfair. I get it. At this point, it looks like the whacko was just a lone whacko. Fine. Be that as it may, the point remains that our political climate has devolved into sensationalistic one-upmanship, fear-mongering and wrangling. How can we say that this has no bearing, no effect on lone psychos out to wreak their own personal vengeance?

Lastly, my heart goes out to the families and victims of this horrible tragedy. They will be in my prayers.

I'm leaving comments open because I think we all benefit from reading varying thoughts, questions, opinions about issues like this. Passion and disagreement is fine, but please refrain from personal attacks. Thanks.