C'mon now SB. His inability and his simpleness is what made him a danger to the family. Of course Vito, Sonny and Michael had to keep him out of the loop at times. But it was not because he was a little creep who posed a direct threat to his family. It was because he was a little simpleton who could innocently pose a danger to his family.

Fredo, like Michael, morphed into this cold and resentful person. His simpleness and hurt was twisted around by Johnny Ola.

If Fredo had gone out on his own seeking to make a deal with Ola and Roth, then I would agree that he was a conniving little creep who was intentionally looking to hurt his family. But that was not the case. Ola and Roth went looking for him because they knew that he was a simple minded person who could be persuaded. They knew that his being simple minded could be used as the ch*nk in the Corleone armor. They exploited Fredo's hurt and resentfulness and turned it into anger.