I perfectly understand how you feel. Particularly during the summer I'm asked to play in numerous wedding parties, and sometimes I'm also asked to make the musical accompaniement of the religious ceremony (catholic churches). I did not have a religious education nor I share the christian belief, so the ceremony is a somewhat strange celebration for me. I always have a slight feel of discomfort, as if I was not part of the whole thing. When approached by a couple and invited to play in church in a wedding, I propose a very light musical act based on well known classical tunes like the Wedding March, the Bridal Chorus, the Ave Maria(s), etc, as I do not known well the specific liturgic repertoires. It turns out that many couples accept and end up enjoying this kind of musical program, although I live in a region with extremely strong catholic influences and beliefs. I never charge extra money for what I do in church (I make it a gift). Hopefully, this summer I met - by chance - an excellent liturgic singer in my town. He sang Ave Maria (Gounod) and I played the music in the church organ. I'll probably put the couples that hire me in contact with him, as he knowns the liturgic repertoire like the palm of his hand and feels much more at ease than me. Due to the nature of the celebration, a person that shares the common belief will potencially do a better job as the musician.

Although having felt a slight discomfort for several times, I never had the sensation that somebody was trying to impose me his beliefs. To answer your question, IF one knows what one's doing (one understands what is going on and the meaning in the different parts of the religious celebration), and IF one does not feel uncomfortable (that is: there is a mutual tolerance regarding one's belief and the community belief - no pressure from each side), I do not consider unethical to play in churches. This seems to me a very personal matter: you have to understand what your conscience tells you.

-- José.