Sue worries that Chris's idealism will make Jim unhappy with his career path. Jim doesn't enjoy his medical practice, as he doesn't find it fulfilling. His patients are needy and whiny, and he doesn't think the work he does placating them is important. Sue thinks that as long as the patients pay their bills, he should be happy to hold their hands and listen to their troubles. Jim has always wanted to do medical research, but it does not pay well, so Sue pushes him to not pursue that path.
Chris is an idealistic young man, and Sue worries that this will rub off on Jim, making him give up his comfortable practice. Even if Jim doesn't give up his practice, Sue believes that Chris's influence will make Jim unhappy, upsetting her suburban lifestyle.