The threat of Athena's baby was clear.
If Hybrids work, they stop killing us, and begin bagging us for farming.
Death or being forced to frakk half a dozen Cylons every day for the rest of your life?
(I don't think they'd use artificial insemination, since the missing ingredient, why their farms all failed, supposedly is love. Although if they drug and hypnotize the shit out of a human being that they might as well be in the Matrix, these dupes can feel a completely loving connection as the doctor centurion milks them for the communal sperm vats with his steel claw... Although it's probably important that the Cylon feels love as well as the human donor. Programming a cylon must be easier than hypnotizing a human? Yup, back to farming. No love required that they can't easily manufacture.)