American troops detested the SS during World War 2 to an extent even greater than how much they resented the regular German Army (Wehrmacht). It was not a war-time bias, but an inflamed, lynching anger which often ended in bloodshed against the apprehended SS personnel.
This passionate feeling happened because of three large reasons.
To start with, the SS were the most extreme believers of the Nazi Party. They had been dipped in the inhuman, vile ideology and were much more savage than other Germans soldiers. They usually did not give up and the combat became much more deadly to the Americans. They were fanatics, as well as ordinary soldiers.
Second major reason is that the SS committed colossal war crime. As the news of the Malmedy Massacre, in which SS troops murdered over 80 of the captured American soldiers, hit the U.S., myriads of units resolved that they would not take prisoners of SS any longer. Both verbal and written orders were given to shoot them when they were spotted. This transformed the hatred into reality and into a lethality.
And, lastly, it was really the case when American GIs entered the concentration camps and freed the prisoners. The terrible sight of the cruel tortures and heaps of dead bodies was a demonstration that the SS guards were not ordinary soldiers; they were mass murderers. To the Americans, the SS was pure evil, that loathing was complete, unredeemed.