I agree with Lilo.

Constantino, killing Sollozzo may have been the right decision, but Sonny certainly arrived at it in the wrong way. He did not have the stragetic goals you seem to credit him with. Regardless of the situation, his reaction would have been to kill Sollozzo. He was like the broken clock which is still right twice a day.

This brings up another question. Tom mentions to Sonny that the other Families might side with Sollozzo to avoid a long, destructive war.

If the Families wanted to avoid a war, why would they side with a relative outsider against the most powerful Family? Wouldn't that make a war much more likely than siding with the Corleones?