At one level, Rabbi Stern’s argument employs some seriously dubious logic – if the essence of life is being able to freely make the right choice without any outside restraints, then we should legalize murder and simply encourage people to do the right thing and abstain. Now clearly this line is a reductio ad absurdum and Rabbi Stern would never advocate doing away with all laws to give human beings the untrammeled ability to choose as they will.
No, laws–in our country at least–are always about right and wrong: they’re about good public policy, which is why religious leaders are sometimes the least well-equipped people to speak out about them. For example: gay marriage is forbidden within many religious traditions but there is no sound public policy reason why it shouldn’t be supported and many reasons why it should. Rather than legislating morality, governments should make gay civil marriage legal and leave it up to individual denominations whether they wish to sanctify these same marriages in a religious setting.
I’m not saying that law should be divorced from morality (and it is clear that religious leaders were at the vanguard of many important efforts to oppose immoral laws, such as slavery or Jim Crow segregation, in opposition to an equal number of religious leaders who supported the existing laws). But the key question is: whose morality? In a multicultural country such as the United States with separation of church and state, there are many different competing visions of morality, which is why the government should not get into the business of legislating any single view, as in the gay marriage example above or as with abortion. Individuals should make their own decisions and should, most definitely, bring in their personal morality, but without trying to foist that morality on the country as a whole.