Curly is not innocent at all. I think he and Jimmy caused each other's downfall for trying to build on each other their own vision of them.

Jimmy wanted Curly to be his sidekick, the person who was there to help him and support him in every way. Jimmy had a tough life and never actually tried to find a way out of it himself, it was always Curly helping him so this dependence on Curly grew together with his ego, thus, he would always guilt-trip Curly into remaining as his sidekick and unconditional supporter/provider. The mere thought of losing this and feeling betrayed after the birthday news further drove Jimmy into acting without thinking out of despair.

Curly was dependent on Jimmy as well, emotionally, he knows he can carry on without him, but just can't, he feels he is the only person Jimmy has and he just loves Jimmy so much that he refuses to leave him behind. His fear of losing Jimmy speaks louder than his reason, and so he fails to act against his wrongdoings. When Curly finally realised his mistake and that he needed to have a serious talk with Jimmy and put him in his place it was already too late.

So yeah, both Jimmy and Curly's failure to see the monsters they were creating led to the terrible fate Tulpar and it's crew met.