The short version is that the Oklahoma Legislature voted to allow a privately funded display of the Ten Commandments on Capitol grounds (the Capitol of Oklahoma, not of the US.) But we have this inconvenient little thing called the Constitution, and its First Amendment, which is interpreted as requiring (among other things) that government treat *all* religions *equally.*
So now the Satanists of New York want to fund a $20,000 monument to Satan--possibly including an interactive display for children--to stand next to the Ten Commandments monument. Fair is fair.
And the quotes from the Satanist spokesperson thanking the Christian legislator who pushed the monument resolution through for opening the door to everyone are just priceless.