Murder is not wrong because I say so, or because a majority of this or that group think so. Murder is wrong because God says murder is wrong (Exodus 20:13). In a blood-soaked country wallowing in mortal sin, many people can be found to support any number of immoral positions. Talking heads can drivel and drone until Jesus' comes back, but they cannot undo one of God's law's or rules or statutes or ordinances.
Even a society that kills 4,000 of its own each day was shocked and horrified by the mindless slaughter in Tucson! Those who ignore the Law of God will feel its severity on Judgment Day, when the Lord Jesus Who died to save all people will come back with all His holy angels. Only those who repent before they die (or Christ comes back) and trust in Him receive forgiveness of their sins and eternal life.
Pray for the victims, the survivors, the murderer, his family, our country, and our world. Pray that they take all of God's Word (His Law and the Gospel of Jesus Christ) to heart. Then remember Jesus' prayer for the men who were murdering Him: “Father, forgive them…”