say ....ummmm...............no
Thank you so much for this wonderful opportunity. I am afraid, however,that this is not the right role for me. I do look forward to future acting opportunities with you in the future, so please keep me in mind.
You could just be truthful. Tell the producer that you think he is great and you would love to work with him on future projects. You just feel that the subject matter of the work is something that you have difficulty putting your soul into right now. Also tell him that you are very concerned with offending him, but you have to stay true to your moral compass right now. Talk to him in person, not email or phone. Then you can read him better and smooth it over if he is angered by your decision to refuse the role. Good luck.
if you are an actor with morality issues you aren't going to go very far. that's why its called acting. You aren't going to church or out for the day, it's your job. There's no way to turn it down without offending this guy, because he's going to realize why you are turning it down, and the natural progression is of course, it will burn a bridge, even if the guy says it won't. Acting is not the field for morality...go be a priest if you are that worried.
Have a personal talk with the director and tell him/her that you can't in good conscience take the role. A lot of actors are able to distance their own personal choices from those they make as actors in order to develop a resume, but it's your choice. A mature person would understand your choices, and he may never make it big. Don't be accusatory when you talk with him and take responsibility for your choice.
I think you should just tell him the total truth, and as soon as possible. The quicker you tell him, the better so that he can hire another actor. Just tell him that the movie goes againt your personal morals, but to definitely consider you for a future role. He'll respect the fact that you stay true to your morals.
If you are ABSOLUTELY SURE that you will not take the role, a simple "No, thank you" will suffice.
Just remember... you may be shooting yourself in the foot. The industry is small (no matter what anyone tells you otherwise) and word gets around. You could be trading your career for a fleeting feeling of moral superiority.
Honestly, the vast majority of actors aren't in a position to refuse roles, and producers know that. I highly doubt that the producer would want to work with you again.
I know that a clean conscience is wonderful, and I certainly don't want you lose sleep at night, but perhaps you should try the role and experience something new. If the scenes you are in are as cool as you say, you just might learn something (or re-affirm yourself).
Break a leg, dearie.
"Thanks for offering such a wonderful opportunity, but on reflection I don't feel that it's really the right role for me right now. I don't feel I could do my best work with it. I love the script and I love your work, though, so I hope someday we'll have an opportunity to work together when the timing is better for me."
i.e. make it about the timing, not about any judgment you have, or else you'll seem inflexible.
I would just thank them for the chance, and just be real with them. Tell them you won't feel right in that part and you don't want that to hender the project. Then ask them to keep you in mind for any other projects that they may have coming up.