Why not? Man's laws apply equally to everyone, and must be followed or legal sanction results. All citizens are treated equally before it.
God's laws, on the other hand, apply only to those who subscribe to whatever particular religion whence they spring. They also have no means of Earthly enforcement. Thousands of different religions exist and are represented in America. However, in a Republic, only laws agreed upon by the majority have any hope of having effect.
A Christian's laws mean nothing to the muslim; his mean nothing to the animist. Man's laws, however, apply equally to all, and are agreed upon by majority vote in our system.
Whatever religious laws one believes in, their obeyance is strictly voluntary. The nation's laws, on the other hand, are not only enforceable but mandatory.
Paul Hill violated those laws. He murdered two people, and said that he would have killed more, including police officers, if they got in his way. He NEVER appeared sad about being "forced to take action"; instead he reveled and gloried in it. He had snide grin right up until the end, enjoying his perverse notoriety.
This places him solidly in the company of OTHER losers who sought such attention...like Ted Bundy, Richard Ramirez, and Usama bin Laden. he just had a different excuse, one which some misguided souls were more than happy to indulge.
We hold these truths to be self evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights . . . We Americans believe that our rights are FACTS OF NATURE and of Nature's God, and thus whether one accepts that fact or not in no way vitiates the existence of the right.
In short, it matters not a whit whether you or I or anybody else accept that the fetus is human that is endowed BY ITS CREATOR (note well, not be any government) with the unalienable Right to Life - that Right exists and is unalienable whether we accept it, like it, know it, want it.
Like the law of gravity, the Natural Moral Law stands outside and above us. All men, and indeed all human institutions, are subject to the Natural Law, just as all objects are subject to Newton's Law of Gravity.