He may have figured that Barzini - a smarter man - would have felt the same way. Tattaglia - a "pimp" -may be stupid enough to make the mistake of getting into the drug trade. Secondly, he felt, like Don Zaluchi, that drugs were disreputable. A pimp wouldn't have the moral standards to avoid the drug trade. but perhaps Barzini would.
It is clear from Vito's statement that he realized someone was backing Tattaglia once Sonny was assassinated - a move too bold for Tattaglia. It wasn't immediately obvious who, so Vito called the meeting to smoke out his true enemy. It worked, and the Corleones won the war.
Sound logic, LW.
But I infer a different conclusion from Vito's statement: "Tattaglia is a pimp. Alone he could never have fought Santino." Tattaglia was a pimp, and couldn't have outfought Santino, before, at, and after, the time of Vito's shooting. So, as soon as Vito regained lucidity after he was shot, he should have figured out that Tat didn't have either the balls or the muscle to mount a war on him. He should have figured that others were instigating and backing the war. And he should have figured that Barzini would have the most to gain from it.
