Would you accept the excuse that?

Would anyone accept the excuse that for a Christian business owner to provide their services for a gay civil union or marriage ceremony is aiding sin and therefore the christian business owner would be committing a sin as well. For example in the Past Yahoo answer has had a Question about what Bible verses tell us not to allow others to stumble. Does it mean that we shouldn't allow them to trip, we should catch them when they fall? Or does it mean that we shouldn't provide them with the tools to sin? The verses that came up in the previous question that I find most valid to this subject were Romans 14:13 ,Mark 9:42. A man named petros mentioned that Paul was referring to Jewish dietary restrictions and that he was saying to not offend those who follow those restrictions on the previous question I am referring to. . What do you think, does it apply to other sin as well?