Isitbullshit: Do cartels really run Mexico, and do they randomly kill Americans?

A few of my friends have advised me not to go to Mexico for vacation because they say the cartels basically run the country now. Cartel gangs patrol the street, and if they don’t like you they’ll just murder you in the spot. The government is helpless because the cartels have high caliber machine guns, rockets, artillery, you name it. I’m told they’re better armed than the Mexican Army, and they’re led by ex-US Special Forces. It’s an open secret in USSF that you do maybe 5-10 years in USSF, then you retire to Mexico and cartels will pay you $1 million/year to lead their dearth squads. Everybody is terrified of the cartels and gives them everything they want because they effectively are the government, and rule with an iron fist.

This sounds pretty dire. Is it true? Is Mexico really that bad?