Why?

Somebody help me understand this. The NYT has an article about Assemblyman Daniel O'Donnell and the same-sex marriage bill (which passed the state house and is now headed for a fight in the senate. In it, O'Donnell is described as telling another assemblyman, Greg Ball: "vote for same-sex marriage, or you won’t get invited to my engagement party." The story concludes:

Despite all Mr. O’Donnell’s entreaties, Mr. Ball, the Republican assemblyman, said he would still be voting no on Tuesday.

But he added that he hoped that Mr. O’Donnell would not cross him off the invitation list for the engagement party.

“I would love to attend, no matter how I vote,” Mr. Ball said.

What I want to know is Why? Why does he think he might be invited to celebrate an engagement he wants to be illegal? And why on earth would he want to go?

Could it be because he's aware that his stand is hurtful to a colleague? Indefensible on any rational ground? Does he want to pretend it's all light and superficial and doesn't matter? That it's okay to say to a man who's been with his partner for twenty-nine years, "you're a second-class citizen who doesn't deserve the protection of the law, but I like you anyway?"

Why would he think any of those things was halfway acceptable?