From his biography he does seem to have a black and white vision of the war, even as a commander in the field. Although this is quite common, many people fighting the war do seem to have a more nuanced view of affairs. mcclellan seems to divide people in awful secessionists and awesome unionists. Thats it.
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"How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?"
Sherlock Holmes in The Sign Of Four (1890), ch. 6