It means they use the money from the sale of oil to do destructive and terrible things.They are suggesting that people do NOT buy oil from those countries.

these are basic meaning of "devastating", this may also help. 1.Sharply critical or damaging "a devastating portrait of human folly" 2.Wreaking or capable of wreaking complete destruction "a devastating hurricane" 3.Physically or spiritually devastating; often used in combination "a devastating blow"