Public opinion these days is that discrimination against a person based on attributes which cannot easily be changed is a problem.
A person may hate anybody they want, but as CEO he was the face of their business. If their CEO had spoken out on the wrong side during the civil rights movement he would also face some social issues. That is probably the closest analogy to what is currently happening with homosexuality. I expect the social consequences of speaking out in favor of discrimination to become increasingly negative.
The main difference between "defending traditional marriage" and supporting same sex marriage is that the former is attempting to restrict the actions of another person based on an attribute they cannot change. In this case it harms nobody to allow two consenting adults to marry each other, so it is difficult to come up with a valid reason to deny them access to the same government processes and protections which a heterosexual couple would be able to legally enjoy.
Separate but equal is also generally accepted to rarely be equal, so marriage it is.
I really do not care much either, as being a heterosexual white male most discrimination does not affect me. Despite that, I do see how unfair it is to deny this to somebody based upon who they love.
If he got his way and gay marriage was entirely banned, it would not affect him at all (presumably he would not consent to marry another man.) He is trying to restrict the freedom of others because he does not approve of who they are, and I do have serious objections to placing that kind of person in a position of power (even at a private organization.)