Is there anything incumbent upon me for having destroyed a gold necklace with a plastic eye, knowing that I did so because it was an amulet believed to protect against the evil eye and envy? And does the ruling differ if the intention for using it was not corrupt?

If it is highly probable that the found object is used as an amulet, then it is permissible to destroy it. For instance, if a necklace contains a plastic eye used as an amulet, then in this case, the plastic should be removed and the necklace kept. This is because the original ruling is that it is permissible to benefit from raw materials once the prohibition that befell them has been removed. As for idols and statues, they must be demolished and their features erased, and it is permissible to benefit from their debris.