While I'm willing to read a book written by a bigot, my general policy is to not give them money. Of Card's books I've only ever read Ender's Game, and the only other book of his I have even a slight interest in is Speaker for the Dead. If I do decide to read that, I won't be buying it new.

There is a big difference between Card and Sanderson. First of all, while I don't agree with the "Ender is Hitler" theory, Ender's Game certainly has some skeevy undertones. Second, Card has basically advocated armed revolution if gay marriage is legalized. Sanderson's nowhere close to that; I wouldn't call him a "bigot," at least.

That said...I have never seen a single good argument against gay marriage. Sanderson says this:

I believe that a prophet of God has said that widespread legislation to approve gay marriage will bring pain and suffering to all involved.

Nine states have legalized gay marriage (ten now with Illinois). AFAIK this has caused no "pain and suffering" there. Sanderson is a smart guy; he knows this. He also seems like a good guy, so his empathy is surely screaming out to him that gay people deserve the same rights as straight people. Why is he ignoring both of these? He says:

I trust those whom I have accepted as my spiritual leaders.

In other words, he trusts his "spiritual leaders" over his own eyes and morality. It's not like he has to do this; plenty of Catholics disagree with the Church over a wide range of issues, for example. In addition, even setting aside the political/moral issue, I don't think his attitude is conducive to good writing.

I'm not opposed to reading Sanderson, but I will admit his beliefs in this regard push his work down on my reading list.