This was my reply to someone having a hard time understanding why a local parish would no longer allow a parishner publicly living against Church teaching to participate in some ministries run by the parish.
It makes no sense to act as a disciple of Christ while consciously going against His teaching. When we comfort the afflicted, feed the hungry, etc. we are doing much more than temporal works of charity; all such acts are ways of bringing Jesus to those that need Him. If we want to do this in the name of His mystical body (the Church), doesn't it make sense that we would do so in an exemplary manner? If you knowingly persist in not obeying a commandment (actively engaging in wrong doing), how can that be seen as anything but a mixed message? I think of it like a drug counselor trying to help addicts while publicly being active in addiction himself.