As I wrote, Marx's critical analysis of capitalism touched on many social topics. You should not be surprised that his work had merit in later social research. You should not be surprised that others who criticize capitalism have overlapping beliefs.
Though do note that "Marxist philosophy", quoting the Wikipedia entry for Marxism, has "branches and schools of thought, and as a result, there is no single, definitive "Marxist theory".
Just like there isn't a single, definitive "liberalism."
> The right are diametrically opposed to Marxism because it relies on an assumption that Man can rise above his Animal instincts.
I ... what? I have no idea what that means. Where does Marx talk about that? How does that have anything to do with class struggle?
> but because of Human nature integration cannot work
What?!?!? English, Welsh, and Scottish cannot integrate? What about Presbyterians and Anglican? Men and women? People with blue eyes and people with brown eyes? Bourgeoisie and proletariat? Gen X and Gen Y?
What does it mean to not integrate when there are different classes in a shared society? They certainly aren't calling for the abolition of class distinction, which is Marx's Communist solution.
> so that the risk of a king is eliminated
Right, so Communism? Otherwise, when there is a power vacuum, something fills it, and without the consent of the people, that's a king, dictator, strongman, or the like.
As it stand, it looks more like the dismantling of the legislative and judicial branches, with all power in the executive.
> given the constraints of the constitution.
I'm pretty convinced the current government does not at all feel itself constrained by the constitution.
> they hope to expand the US to other countries voluntarily
History shows the US has a long history of not expanding voluntarily. What's changed? How has this new right de-fanged itself from the tendencies of the old right, like Andrew Jackson, that they seem to admire so much?
Many Christians also align with liberal and even radical thinking. Integration is possible because everyone is a child of God, and "When God’s people are in need, be ready to help them. Always be eager to practice hospitality.” ... “The foreigner who resides with you must be to you like a native citizen among you; so you must love him as yourself, because you were foreigners in the land of Egypt. I am the Lord your God.”