Because Indiana is the state currently getting all of the bad press over this. Indy is arguably the biggest convention host city in the U.S. If these conventions decide to take their business elsewhere it becomes an economic issue.
When outside tax revenue dries up, where do you think the legislature will turn to make up for it?
i agree it shouldn't be dismissed so lightly, but I have to support the law purely based on the business owner's right to deny service to anyone they wish. Black, white, gay, atheist... It's their right, regardless of how distasteful it may be. Now, the state should make as much of an effort as it can to retain these conventions, and I'm sure "green" will trump "ideology" in most cases. There needs to be a mafia style "sit down," to hash out acceptable conditions.