Just to clarify, I think we have to make sure to point out that the reason behind many Christians' propensity to encourage modest dress has nothing to do with tempting boys but with safeguarding a woman's self-respect. As you say, "[G]irls and women constantly receive the message that to matter, they must be sexy. On this same hand, some women will dress in an intentionally provocative way because they equate self-worth with attention from men." In my own personal experience, I think encouraging women away from this path is the more usual intention behind promoting more modest dress, though I don't actually hear about this topic a lot at church. (As an aside, if girls shouldn't wear tight or low-cut shirts because they're too sexy, boys shouldn't wear tight pants. It's only fair.)