To suggest that Tom has indicated to Sollozzo that the Corleones may be interested is a stretch. If nothing else, that would be very out of character for Tom.
When Sollozzo kidnapped Tom he said, "Sonny was hot for my deal, right? And you knew it was the right thing to do." How'd Sollozzo get that impression? Not at the meeting. But he must have been in contact with Tom several times prior to the meeting, and have gotten some hint from Tom that Tom thought it was a good idea.
There's no reason to believe that Tom has the ability or inclination to force Vito into a meeting he does not want to have. And the meeting wasn't the problem - the refusal was... Tom's counsel was ultimately irrelevant in the ensuing events. I don't see how Genco would have been able to forestall the impact of narcotics on the Corleones or the Cosa Nostra in general.
Of course Tom couldn't force Vito to have the meeting. But Tom's advice and persistence for Vito to not only have the meeting but to approve drug trafficking had to have had some influence on Vito.
I agree that the drugs business was bigger than Vito, and that Vito should have realized it and gone along in some way, or at least not opposed it, for the safety and security of his family. In the novel, Vito asks Tom: "What did you think of that man?" Tom replies: "He's a Sicilian"--meaning that he wouldn't take no for an answer. That's when Vito told Tom to send Luca to see him. And that's where Vito made his big slip up--telling Luca to do the pretend-thing.
This raises two questions:
1. Could Vito have stopped drug trafficking? No--too much money in it. But he might have delayed it. He could have told Sollozzo that he'd have to think about it. Meanwhile, he'd arrange for Luca to meet Sollozzo to discuss terms. Luca would arrange a meeting among himself, Sollozzo and a drug dealer of Luca's acquaintance. Luca would murder the other two and make it look like they killed each other over a drug deal gone bad. No one in the Families would have been deceived, but that's what Vito would want: A shot fired across their bows. Tattaglia, the pimp, would have to suck it up. Barzini would have to bide his time. He'd still be hot to trot, but with Sollozzo dead, he'd have to wait for another wholesaler to approach him. A temporary measure, to be sure, but one that would have worked over the short term.
2. Suppose Sonny hadn't shot off his mouth--would Sollozzo have tried to kill Vito anyway? I think Sollozzo would not have taken no for an answer. But, with no obvious ch*ink in Vito's armor, he'd have a much harder time persuading Tat and Barzini that killing Vito would get them where they wanted to go. It'd be all-out war with a vengeful, no-drugs Sonny, instead of a possible deal with a greedy, pro-drugs Sonny. I think a more likely scenario would be for Sol to convince the heads of the Families to call a meeting like the one we saw later, to persuade Vito to give his approval. That might have worked. But Sol would have lost a lot of clout because he'd have to rely on the other families to do what he failed to do.
