The 14th amendment only prohibits state action, not private action.
Murderers are prosecuted under state laws defining and prohibiting murder, not under the Fourteenth Amendment.
Stretch your mind a bit.
If the former Confederate states had passed a law saying that the killing of uppity freedmen was permissible under certain circumstances, that would not have been permitted to stand, even though the murder statutes remained the purview of the states—any such exception permitting the slaughter of freedmen would have been struck down.
Similarly, any exception to criminal law permitting the slaughter of the unborn is a similar violation of equal protection. A state cannot morally distinguish arbitrarily between differents classes of persons in its laws with regard to the protection of life without a compelling state interest.