Namor's actions also could've killed the planet, he sent Thanos to where the bombs were too. So namor was justified in trying to kill the Wakandans twice now? And why should BP warn them first? So that the attack could fail and Namor could try to kill them again? He did the right thing by recommending that they not pursue war, not sure what else he was supposed to do. Namor was reckless and stupid even in Doom's eyes because he chose to free Thanos and his gang and Terrax. He did the best thing available by blowing up those Earths, but he had to pay at some point.