I think Hobby Lobby's customer service should have not gone with the we know Christ is the only way to Heaven approach. Why? Because people often go through a great deal of searching and work to find their religious beliefs for themselves. So when you say, Christ is the only way, you seem to be looking down on their religious beliefs, and that feels like an insult to many people.
I understand it can be difficult for those reared in places where religion is a public matter to understand this world view. However, often we must be sensitive to other world views in our customers. Some people see being given a discount as an insult. This is not my world view, but it's an understandable vision of the world that does not in fact harm me. To many, religion is very personal, and telling people what religion they should be is as bad as telling them what sort of underwear they should wear.