The crux is that you really shouldn't have laws that infringe upon the rights of those that differ from you.
That said, I think that there shouldn't be a law that forces you to conform to activities that are against your rights.
So, while I don't think that there should be a law that says that businesses cannot be open or sell alcohol on Sunday, I also don't think there should be a law that forces that store or business to do so.
In other words, such decisions should be in the hands of the business owners and the community. If a community/city decides that stores should be closed on Sundays, then that's the "unwritten law" that the community chooses to live by.
Some people would argue that it's a person's "right" to buy alcohol whenever they want it. I would concede to that... but at the same time I would say that if there are no stores in your area that sell it, you are out of luck, sorry.
Obviously, this can be abused, too. If a store chooses not to sell beer to a person of Asian descent, for example, then this is race discrimination and should not be tolerated. If you offer a service (like selling products) then issues of race/gender/religion should not be grounds for denying service.
It all comes down to common sense... (something lacking in today's society)... if Bob's hardware is closed on Saturday because he likes to go fishing that day, then so be it. If Munchy-Mart is closed on Sunday because it's a Christian-owned business then so be it. If Jack's Liquor Shop wants to sell booze on Sunday, then so be it.
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
Separation of church and state... the government can make no law even related to religion. However, if a community, city, state, etc. chooses to prohibit the sale of alcohol on Sunday, then they are within their rights to do so as long as it is not with respect to religion.
This is off topic, but this could easily become an argument around the Ten Commandments issue. Having the Ten Commandments hanging on a wall of a courthouse or a pedestal in the front lawn isn't even law related. There can be no law made prohibiting it, nor a law endorsing it. It can just be... for no other reason than the majority of people want it to be there.