Compassion, Forgiveness, Sympathy – these are big ideas in Middlemarch. Part of Dorothea's problem is that she feels too much. Both "compassion" and "sympathy," if you look at the root words loosely mean, "feeling with" someone. Dorothea feels with everybody, and she can't turn it off. Is it possible to feel too much compassion and sympathy, or to forgive too easily? This is a big question in Middlemarch.
Although "fellow-feeling" is important to the moral code of Middlemarch, an excess of it, like Dorothea's "fanaticism of sympathy," can lead one to sacrifice one's own happiness without cause.
Although Dorothea's sympathy might be excessive at times, she is still held up as an ideal to which all others should aspire.