The Ostheer Generals would never commit to an overthrow of Hitler because of the potential accusations of a "stab in the back" by officers associated with the Army in France. If you were in the Wehrmacht Resistance, you needed Ostfront Officers who were respected by the front soldiers like Manstein and Guderian to form the core of a new Government.
Yes, say what you will about Harry Hopkins and Dexter White, all either Soviet Fellow Travelers or, in White's case, and outright spy like Hiss, FDR had sound reasons for staying out of coup plotting. After the conduct of the SS, the SD, the Einsatzkommandos and the Wehrmacht itself in the East against Russian civilians, the notion of dumping Stalin without earning 100 years of Russian enmity was too much of a price for FDR to pay.
In the long run, FDR did the right thing. Yes, he was surrounded by Communists, but that doesn't alter the fact that in failing to support a largely amateurish and bungling gaggle of Junkers coup plotters, he did the right thing, perhaps for the wrong reasons.
That said, Canaris deserves the honor coming to him from the State of Israel.
There were, as well, the frightening consequences of failure that did, in fact, take place. The Nazis tortured people to death - Hofacker - or hanged them with piano wire - Stauffenberg's brother - or simply executed their relatives. Physicist Max Planck's son was killed for his involvement. Involvement meant risking one's own life and those of one's family. That's how police states maintain themselves.
And so the most necessary part - what would constitute a post-Hitler government - was something that was incredibly risky to plan and, in fact, wasn't thought through with sufficient thoroughness. That I can forgive them. They tried to slay the monster and failed. But they did try.