Um, it's wrong, but only because of the particulars of this example, in that the board is probably racist. And to close the loop on your example, it would be open season on the board once public opinion caught up with them.
I think you're presupposing that principles are interchangeable and I don't accept that. I believe in some inherent human rights, and the merits of this particular issue are incredibly relevant. The gentleman in question made a substantial monetary contribution aimed at denying a collection of people a set of privileges.
The reasons for why society ought to privilege views like his over the rights of other people are flimsy at best; it's just a lousy idea given that the basis is wholly religious. Substitute something interracial marriage if you prefer. The fact is that some views are not just immoral in the face of society's avowed principles but unsound as well.
So you're arguing my general argument is invalid because in the specific example I use, you claim the board is racist. You then go on to claim that social principles aren't interchangeable and public opinion would eventually obliterate them. My question is, if public opinion has always been and always will be anti-racist, how did so many racists get on the board of not just a single company, but the majority of companies in the 70's? Not to put too fine a point on it, but your belief that principles aren't "interchangeable" (I think you meant "changeable" or "subject to change"?) is provably wrong.