Don't forget that Tom also never thought that Sollozzo and Tattaglia would smell a rat when Luca Brasi of all people said he was unhappy with the Corleones (granted, neither did Vito, but isn't it the job of the Congligieri to point those things out to his boss, even if the boss doesn't listen), he didn't think that Sonny was being set up by Carlo with the final beating of Connie, he perhaps didn't think that the lure of drugs would be too much for some people (i.e. Paulie Gatto) and something should have been done to increase the stipends those men were getting to keep them from getting involved in the street trade (or in Paulie's case from selling out; I'm sure he was promised something in return)
I don't think Tom was even informed about Vito's plan to send Luca to find out what was underneath Sollozzo's fingernails, so you can't blame that one on him. Also he did not know about the set up with Carlo, athough he did try to stop Sonny from leaving the compound at the risk of Sonny running him down.
