Well, one one hand, it's his right to say so.
And it's the right of people who disagree with him to punish the thousands of employees employed by him by not going to one of those restaurants, and thus perhaps sending this store or that out of business.
What is not okay is for the mayors of cities to say, "Okay, we're going to shut you down, we don't want you in our town." Apparently Rahm Emmanuel touted Chicago values in his comment - which is odd considering what Chicago values stand for - highest murder rate in the US, in the black community most of whom are also against gay marriage!
Rush mentioned that yesterday...will the Mayors of Boston and Chicago dare to tell the black religious leaders who protested against gay marriage to leave their towns also?
What is not okay is for student groups to demand the restaurant be removed from campus, or whatever.
Shouldn't that be up to individuals to decide, for themselves? Leave the restaurant there and see who goes into it. If it makes money, it stays, if it doesn't, it doesn't. That would be a fair test (assuming that groups of students dont' gather outside the restaurant and Chikfila-shame anyone who tries to go in.) Yes, I myself am for gay marriage, but I'm also for freedom of speech. If people choose to not go to Chik-fil-a because of what was said (and I don't go to it because I dislike the name, and anyway, Kentucky Fried Chicken is superior!) that's their business, and that's all that should matter.