No one is suggesting even remotely that renting an Imax theater to someone implies support of the group so the question of government involvement with religion was never an issue. It was the purported association of the Smithsonian and a certain viewpoint in someones mind and the honoring of a valid contract that was the issue at hand.
I have as much legal right to use the public, paid for by taxes, street for a religious or other opinion parade as the most irreligious, secular group in the world even if the city doesn't like my viewpoint and they are bound to honor a contract with me even if a museum doesn't like it.
The Center and it's actions were wrong.
The courts will decide that. Until then it isn't news.