Anything other than that would have to be an act of choice. (Even in cases of rape and incest a choice is made on the part of the perpetrator) Every time one participates in the marital act, even those outside of marriage, they are making a choice that may lead to pregnancy. The act on their part is not an accident, it is a choice. Even with the best birth control, there is still a chance that conception may occur. The baby that is conceived is not an accident, it is a choice.
Since this is a matter of choice -- no one is told they must engage in the marital act -- why should others be expected to pay for this activity? There are sources out there that tell people they are being responsible if they use contraception and want to prevent a pregnancy. Being responsible means taking control of yourself. If one does not want does not want a pregnancy to result from the marital act, don't engage in the marital act. There is nothing accidental about becoming pregnant.