I think that the greater political success Romney has, the more damaging it is to his cult religion.
The one thing all cults fear is scrutiny. The more publicity Romney has, his religion of choice will also experience a corresponding amount of publicity and scrutiny.
Think about it...an undecided voter hears Romney's name and maybe a few points from his platform. This voter looks a little deeper to see if this guy is someone worthy of consideration. Somewhere along the way, Mormonism is going to come up, and this voter actually wants to know what it means to be a Mormon.
And now the cat is outta the bag...Mormonism, complete with it's shady history and nutty beliefs is now on the table for examination.
This hypothetical individual might even like Mitt Romney and agree with his platform, but what is done cannot be undone. One more person knows about Mormonism and probably read material from Mormon 'Apostates'. Cults thrive on ignorance, and a cultist politician does the most harm by opening his religion up to examination.
I'm a Republican, and I won't vote for Romney. It has nothing to do with religion. It's because he resembles a used-car salesman