"If stopping the killing of human beings ( as defined by those opposing abortion) is NOT a reason to have laws, please let me know what is?????"

This is a valid point, but it doesn't even have to be "stopping of killing of human beings (as defined by those opposing abortion)".

Your point is just as poignant if one were to point out that the definition doesn't have to be any stricter than to point out that we don't know that a fetus is NOT a human being and thus, the burden of proof should fall to those who want to kill it, to prove that it is NOT a human being.