Actually, that would be a tough argument to make. Every conservative writer in America and the entire conservative base was convinced that John Roberts was a conservative, and that based on his record, his testimony, his early votes, etc.
EVERYONE....that is why the shock at this.
So, I'd have to agree that Occam's Razor is on Marlowe's side, at a minimum in terms of Roberts never having presented in the past as a liberal.
SOMETHING took him to liberal-land...and that's what Marlowe is "Occam's Razoring" about.
It's entirely possible he woke up one day and said to himself, "John...darn...they're right. Those darn liberals are right. I'm signing on right now as of today."
I guess that's a possibility, too.