Atheists don't go around insisting atheism=conservatism. And you have never yet explained to me what "individual sovereignty" is. It sounds like one of those self-serving, made-up phrases like "social justice."
What is individual sovereignty, to you?
I don’t want to distract you from the initial point.
To answer your question, historically the concept of individualism has been juxtaposed with that of collectivism. But I think the correct analysis is more complex than simply that Marxist ideology favors collectivism while its primary opponent—American conservatism—favors individualism.
First let me say, collectivism amounts to mob rule and is a treasured tool of tyrants.
The way I see it, individualism can also be overemphasized. That is, absolute autonomy of the individual would essentially lead to a form of psychosis.
American conservatism is based on the idea that individuals possess sovereign rights—the sovereign part means that the group cannot legitimately violate those rights merely for its own interests. The foundation of our society also includes reliance on particular aspects of community, such as church groups, political entities and the military. This intricate balance between group and individual is the basis for the American political system, and it is what the leftists are trying to overthrow.