The following two positions are consistent with one another.
1) Abortion is murder.
2) The Constitution, properly interpreted, makes it unconstitutional to outlaw abortion.
The arguments for 1 are never identical to the arguments against 2. Arguments supporting 1 do not prove that 2 is false. So 1 and 2 are compatible.
Of course, the Constitution is amendable. Arguments for 2 involve trying to show that the right to privacy is not absolute. The argument is never that the personhood of the fetus is provable.