then let men kill which cannot share, let blood and flesh be mud and mire,
In a poem that has been generally positive, we suddenly get a swirl of dark images.
We've got dudes who kill people because they're selfish, and then images of "blood and flesh" becoming "mud and mire."
You could interpret these two lines as being about the wars of the world, some of which blow up when one country marches into another country and is like "Give us your stuff."
This muddy, bloody, fleshy thing definitely reminds us of bodies piling up in the muck of a battlefield.
Why is the speaker bringing this up now, though? Could it be that he's trying to get across the idea that his father is leaving the evils of the world behind?
scheming imagine,passion willed, freedom a drug that's bought and sold
It looks like we're hearing more about the evils of the world here.
"Scheming" isn't a very nice thing to do, but lots of people do it to get what they want. What's worse is these guys are scheming for "imagine,passion," which we take to mean desires that aren't even real.
Notice how Cummings takes the space out after the comma, making one of his patented squished words. The effect kind of blends the meanings of both words in our minds.
So, it's a passion, but it's imagined, so it's not real. See?
Man, what a stupid thing to scheme and backstab for.
Next, we hear about "freedom" being "a drug that's bought and sold." Could this be some kind of comment on America?
The idea of personal freedom is an essential part of American identity. Of course, our economic system of capitalism goes right along with that, and some accuse that system of being unfair, because the rich inevitably control it. These people say that the idea of personal freedom is just a sham used to control the lower classes, and it's sold through various clever marketing schemes.
At the time Cummings wrote the poem, there was a ton of debate between leftists who were more into communist ideas and right wing people who were more staunchly capitalist.
Whatever the case, the father is moving beyond all this debate; he's leaving the contentious world behind.