Pak Mudi, without digressing into a full blown discussion about theology. which i think would be inappropriate in this forum, Catholicism does not embrace animism as it sees these spirits as only being evil and destructive. Therefore only an evil spirit would be able to inhabit a keris. This is not an acceptance of animism, it is a rejection. This is not how animism is dealt with in Indonesia. While there are cetainly bad spirits there are also good and helpful ones. It is heretical in the catholic faith to listen to or use these spirits to help you in your life regardless of how you might personally view the goodness of any particular spirt. This is just brushing on the differences, but i hope it helps your understanding.
Thank you Alan for a very clear, concise, no nonsense explanation on the magickal and mystical relationship of keris and man.