Not to bring the unfunny, but - while forcing kids to kiss old relatives/anyone may not constitute rape in and of itself, it does run counter to teaching kids the "no one may touch you against your will/in a way that makes you uncomfortable; if someone does, tell an adult you trust" principle that may one day protect them from molestation. Personally, I'd rather have Aunt Minnie be offended that my [as of yet hypothetical] kid rejects her sloppy kisses and have said kid live with the understanding that her physical boundaries are sacred and she has a right to speak up in defence of said boundaries.