If I understand you correctly, the premise you must present is that it is immoral to pass laws based on a majority religion for the purpose of curtailing certain behaviors and encouraging other behaviors that are unique to the majority religion, i.e. no consumption of alcohol, no use of tobacco, mandatory attendance to the place of worship of the majority religion, so-called Blue Laws, censorship of reading and viewing material deemed unfit by the majority religion, etc. Am I correct?
You can eliminate the argument being defined as laws against murder, rape, theft, etc. by pointing out that those laws transcend any one religion, because no society can long endure if those kinds of actions are sanctioned or encouraged, or even just allowed. Those laws are not "moral" laws, per se, but common laws needed for a society to function. The issue of morality in laws must be seen as an attempt to force people to live by the moral standards of the majority religion, whether or not they choose to believe what that religion teaches, and in actuality those types of laws are passed so that the members of the majority religion don't have to deal with those who don't share their beliefs. It is born of an arrogance and a desire to control others who don't believe as the majority does. That attitude is immoral in and of itself, because it violates the majority religion's prohibition of prideful, arrogant and presumptuous behavior.
As for the Supreme Court cases, Any attempt to coerce an individual to violate his own morality to satisfy the needs of an opposing Morality, or to be forced to observe practices which are contrary to the person's stated beliefs is a violation of the majority religion's stated belief that "whosoever will" may come. It also violates the majority religion's viewpoint that outward actions are not what will redeem the person, but inward acts of the heart, and that the Supreme Diety is not fooled or swayed by the outward behavior of the people, no matter how it was accomplished. Legislating morality actually violates the very religion that instigates it.
Hope this helps...