Is politeness of any use in this situation? Is the answer not, 'I don't want to have sex with you'?
Compatibility and suitability could only be truly assessed by having some kind of relationship with someone else. This would at least require a face to face meeting, to establish whether or not such conditions existed or were likely to develop.
Making a decision remotely, denies yourself and the responder the experience and the opportunity to see if you are or would be compatible and/or suitable. Its undemocratic etc.
That is the most dissapointing and infuriating facet of such a rebuttal. It leaves so many people feeling inadequate, powerless and exploited. Which you wouldn't do if you cared about someone.
So it remains a clumsy process.

Because of this I expect most people don't reply. Its probably the safest option as you don't become the 'cause' or fixation of the dissapointed responder.