(Spoilers All) The RLJ Theory: a sure thing?

Excuse the ignorance please, this is a legitimate question.

I'm not proposing an alternate theory, but after spending significant time on this subreddit, I've noticed a pretty large volume of people speaking of the RLJ theory as canon, but is it really confirmed?

I've read through the books only once, as well as the Dunk and Egg volumes, so I'm not as educated in ASOIAF as most of the other contributors on r/ASOIAF, but I have come to realize that once you start assuming surety in GRRM's story lines, it tends to bite you in the ass.

Could it be possible that this is just one giant red herring? Is there any evidence to contradict the mass following of the RLJ theory? The skeptic in me hopes so.

I'll prepare to be violated with downvotes.

EDIT: I was worried that this would only serve to confirm the widespread subscription of the RLJ theory, but thankfully a few alternate theories and discrepancies surfaced. Thanks for your contributions, they will certainly aide in making my reread even more interesting.