Needlessly alienating potential allies

In light of the recent protests against Target and Best Buy, people are asking whether we are needlessly alienating potential allies. Some people say that this is not a serious worry, since the anti-gay crowd will find any reason to oppose us, while those who already support us will still do so. Nonetheless, one problem with the "preaching to the choir" mindset is that not everyone is in the choir. How shall we regard the fence-sitters or those whose support for us is wavering? If everyone's mind were already made up, what would be the point of protesting at all?