In Swamp Thing 50, Swamp Thing basically convinces the Great Evil Beast not to invade heaven by answering it's query about the purpose of evil: Swamp Thing replies that evil exists to balance out good. He gives the example that the Parliment of Trees provided him in issue 57, of a ladybug dying in order to fertilize soil. The aforementioned can be seen as an example of a necessary evil, but it conflicts with the examples of evil seen in previous chapters of the American Gothic storyline such as racism, misogyny, and serial murder which don't lead to anything fruitful and in fact are quite senseless.
People might say I'm overthinking it, but the themes presented in the prior issues of Alan Moore's Swamp Thing are so fully realized that I find the conclusion to American Gothic disappointing.