In The Interest of Gender Equality
Seriously. At least Belinda sat with the Tories for a year - you could make the case that she didn't feel comfortable in the caucus, or wanted to avoid an election, or had a ideological difference with the party. I certainly didn't make that case and was fairly critical of her, but that's an argument one could make.
In the case of David Emerson, he was elected two weeks ago as a Liberal. There is absolutely no way to spin this, except as a case of blatant opportunism.