Like mustachepete, my biggest opposition to your theory is in regards to your first instance - the McClusky/Sollozzo hit.

I don't see the police commish being shamed into helping Vito. Not to say no action would be taken against McCluskey but that would not turn Vito into a sympathetic figure. He was a criminal, and that was that in the black-and-white world of law enforcement. There was nothing that could be done that would allow the Corleones to benefit from the police.

As to your other main point, while McCluskey could be disciplined/shamed into becoming a non-factor, Sollozzo would have merely found another time and manner in which to strike, one that would likely be effective, as he was both intelligent and driven. He would not have been deterred by anything other than death.

I do think your other openings are more plausible, but by then, Michael had not only become a killer but witnesses the killing of the true love of his life, which hardened him to the point of no return, hence the choices he made from that point forward.