I am a Reiki master as well, and the Churches viewpoint may be based on ignorance but their conclusion nevertheless has some validity. The reason I say this is because because 'spiritual' is not the same as 'harmless', 'always beneficial', 'always good'. Any spiritual practice can open one to good and bad influences. It is just like medicines, natural does not mean not poisonous and if taken in excess even water becomes toxic.
The problem with Reiki is that when an averse reaction sets in most Reiki practitioners don't know what's going on. Their psycho-spiritual knowledge is limited or one-sided and because there is no organizational structure for Reiki there is also no referral system.
What other choice does an affected person who is overwhelmed by spiritual energies have other than contact the established and traditional structures?