We all have to make our own decisions on these issues but I know that this has put a damper on my enthusiasm to see this movie. To tell the truth I would have the same concern if it was revealed that the actor was an open womanizer or adultery so it is not the issue of homosexuality. In actuality it is the activism of Allen and that a story of men who were committed to Christ would be used to promote an agenda that is anti-Christian. It is not even the issue of sin as we all sin but it is the fact that Allen does not find fault in his sin and even wants to promote it. There is a vast difference between one who sins and is convicted by the Holy Spirit and is in the process of change and one who relishes and denies what they do is sin as Chad Allen seems to do.
Jason Janz at Sharper Iron writes on this subject that may give more insight. If you do not see the movie I would recommend seeing the documentary Beyond the Gates of Splendor.