I'm not so sure TB. For one, it violates Vito's exhortation that one should never let anyone outside the family know what you're thinking. By refusing to accomodate Geary's attempted extortion, he simply alerted Geary and opened the gates to any number of negative possibilities. As viewers, we have the luxury of knowing the outcome. But Michael couldn't know at that time that Geary could or would be be entrapped.