St. Thomas Aquinas refers to this when he asks
whether human law should forbid all vice. It cannot
he says, “because human law is framed for a number
of human beings, the majority of whom are
not perfect in virtue. Therefore human laws do not
forbid all vices, from which the virtuous abstain, but
only the more grievous vices, from which it is
possible for the majority to abstain; and chiefly
those that are to the hurt of others, without the
prohibition of which human society could not be
maintained; thus human law prohibits murder, theft
and such like.” Of course, we see
abortion as murder, but the problem is that many
others do not. We do not even have consensus on
the moral status of the early embryo. Therefore
overly restrictive laws which the majority of people
will not respect end up bringing about even worse
evils. p 34
chausa.org/docs/default-source/hceusa/winter-2017—full-issue.pdf?sfvrsn=8