With that same logic, why should childless couples have to pay taxes for schools at all?
Because we all benefit from roads, science, medical, pharmy, computer, arts, teachers and so on and so forth. Tax dollars spend on education return to all of us, either directly or indirectly.
However, if I'm Buddist, Mormon, Baptist, (insert group here); I do NOT benefit from paying from a minister who serves a congregation I do not attend. The recipients of the minister are limited only to the congregation to which he belongs. Doctors, engineers, programmers, teachers, ect... serve EVERYBODY regardless of religous belief (and this is enforced by federal law).