One flaw was the fact that I didn't mention that since the Children talk more about their biological parents, Karp assumed the children were brought up primarily by their parents
You're smart to have caught this omission.
This paper is a bit too short for an upper-half score.
Make a list of missing points of evidence and post them here in bullet form.
Post them here.
Here's what I mean:
what the given argument lacks is the details of his analysis,
This is really the main idea of the essay. (It should have been your thesis.) Your job is to identify
which details are missing and then tell me how their absence weakens his argument.
You've partially accomplished the task but your discussion wanders around quite a bit.