Let's lead off by pointing out that he entered the life of a woman who seemed to be going places in this world under by posing as something he wasn't. As Mike describes it, once he took his uniform off, the dashing, laughing love interest revealed his true self: a morose, miserly, distant clodhopper who regards women as pretty much put on this earth to do chores for idiots like him and who thinks that cooperation is synonymous with castration.
The second interesting fact is that his great big plan for the future can be charitably summarized as the fever dream of a mentally deficient opium fiend. He had no idea how to run his farm, no business ruining the lives of his family doing so and no intention of manning up and calling it quits despite stupidly managing to bury two children because he didn't want to take charity. As Mike said in his letters, his need to have an identity loomed larger than sense, decency or the needs of others.
This leads to his callous disregard for the needs of the unfortunates stuck having to deal with him. Mike might think that having to live Sheilagh's needlessly miserable existence made her a strong woman but all it served to prove is that she found it difficult to rid herself of a very horrible and worthless man who resented the wife who wanted love he couldn't give and the horrible, ungrateful children who made his life a misery by being born weak and dependent.
The odd thing is that Mike has no real idea that when he said that he WAS Harvey Rood, he was one hundred percent right. He, John, Phil and Anthony think that they're something they're not, they hate sharing, they have a self-serving I-it view of women, they don't have the least idea how to live their lives and they resent their children for making them incompetent.
The reason that he fails to see this is that he's so used to the idea of that horribly brutal gender war I talk about to see how like Harv he himself is.