Could you perhaps link to the relevant comment so that its claims can be better addressed? As you have presented it here, there is an issue with the Premise, which may be conflating the broader use of Concentration Camps from 1933 onwards with the attempt at mass extermination of European Jewry which only began in 1941. That is to say, the average citizen would of course not know about the extermination camps prior to 1941, as Chelmno, the first extermination camp, was only built in the fall of '41, and by dark coincidence began operations the day after Pearl Harbor; and likewise, while the Einsatzgruppen had been operating in Poland in 1939, the 'Holocaust by Bullet', as the pre-camp phase is sometimes termed, is generally associated with the beginning of Operation Barbarossa.

There is much that can be said about awareness of the Holocaust after US entry, and of course awareness of the mistreatment of Jews, more generally, prior to WWII, but as specifically stated, the US couldn't have obscured the existence of the Holocaust prior to 1941, as the Holocaust is generally considered to have started in 1941. I'll respond to this comment with our Holocaust Macro, which will provide a little more background on this all.