User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-170.235.245.55-20130515184939/@comment-3146930-20130515202459

She didn't take their memories away because she was worried they wouldn't help each other's camps. She took their memories away so that the camps wouldn't know they were Greek or Roman. Camp Jupiter for example seems to hate the Greeks, especially Octavian and it is shown that he can stir up a crowd. It is also shown in The Mark of Athena that even after several months, Annabeth still doesn't trust Jason and feels he could be leading them into a trap. If each camp found out, Percy and Jason would most likely be tossed in jail or whatever.