"I told you I can handle it, I'll handle it" implies that Mike had the choice to not whack the 5 families. Vito surely gave him plan B, but Mike agreed to go along with plan A and all the consequences that would follow.

I agree with Turnbull except that I don't think Mike could have ever told his pop 'handle it yourself, im outta here'(never leave a man behind).

And I still think that Mike always had the intent of getting out/becoming legit. Problem is that he was soooo competitive that it was not good enough just to 'get out/become legit', he had to 'get out/become legit' to the VERY best of his abilities. Thus whacking the 5 families, conglomerating a gambling empire and fighting against the vatican.

In the end this competitive fire burned him, he flew himself and 'the family' too close to the sun when he could have turned back long before(after part 2 for example).