The only really bad green corruption card IMO, is Nightmarish Visions: lose 2 sanity and gain 2 clue tokens, and even it might be good in some situations. The others tend to restrict cooperation but give good abilities and benefits in exchange. Most of the penalties are drawing more corruption or discarding corruption which bring you closer to drawing Red Corruption cards. Now if you get to the Red corruption cards, the are almost universally bad. I think the set is quite well designed.
The cult encounters, however, are quite dangerous. But you don't have to go into the woods, etc so those are easily avoided. I've always joined the cult when I have an opportunity (3 times) and its mostly benefitted me and the group.
However, the herald is very tough, IMO. Especially with monster surges bring on doom tokens and the extra tougher than average monsters. I haven't yet beaten it when I follow all the rules. But I haven't lost because of the Green corruption cards.
The last time we played, we didn't use the Pagan Rites, ie doom tokens on monster surges and we won. In a normal game, we usually have 3 or 4 surges and adding that many doom tokens alone would probably cause us to be unable to seal most of the GOOs.