I think the attacks on police/authorities in general in Mexico by the cartels are what is most disturbing to Americans. Our country has not experienced anything remotely approaching this level of violence toward authority since the days of the "wild wild West" and, to a lesser extent, the 1930's. There is no question that it is dangerous to be in law enforcement or to take any government position and oppose the cartels in Mexico. Many brave Mexicans have given their lives to try and break the cartels. Whether they can succeed or not, who knows? As long as American money buys the drugs, there will always be people willing to battle law enforcement to try to get a share of those American dollars, and in the U.S., we have certainly not eliminated the drug trade, though we have driven it--more or less--into the shadows.
Granting all that, we find Mexico safe for tourists (and we live 30 miles south of the San Diego/Tijuana border. Those who do not go where they should not and do not attempt to buy drugs are not targeted. There have been a few, very few, instances of innocents in the wrong place at the wrong time, but as the poster mentioned about Indiana, innocents are victims in the U.S. too. Examples of violence in Mexico have been played, replayed, and replayed in the U.S. to the point that it seems as though tourists are being gunned down on main streets, and that is not the case. We have seen American media report incidents of "3 Americans" or "American teens" killed/kidnapped, etc. in Mexico; however, the media never comes back to report "The three Americans killed in Mexico have long criminal histories in the U.S., and were involved with the cartels in Mexico," or "The American teens were smuggling drugs across the border for the cartels." It would help if the whole story were reported, rather than simply sensationalizing the initial violence. The violence is real, but we would not go to our 2nd home in Mexico if we felt unsafe: we're still spending more than half of each year there--and we're close to Tijuana and the border.
Americans tourists typically do not speak Spanish; American tourists are not used to seeing a military presence on the streets (though those who have been to Israel--where the crime rate is lower than the crime rate in Seattle--have seen them); American tourists are certainly not accustomed to law enforcement being a target. All these things combine, I think, to make the violence, which is real, in Mexico seem more horrific than it actually is. At the heighth of the drug war in Tijuana a year or year and a half ago, the murder rate in Tijuana was lower than the murder rate in New Orleans; it was not far above the murder rate in Washington, D.C. Yet because these cities are in the U.S. and we are within our comfort zone, we accept that violence.
I believe Mexico is still a safe place to be a tourist, but as the poster from Indiana said, you must take precautions at a conscious level--perhaps the same precautions you take at an unconscious level in the U.S.