I’m not really a fan of this argument. At all.

One, it treats belief in the plausibility of the prophecy as a given, easy and effortless and reliable to the point where two women – Lyanna and Elia because this argument only creeps up when someone wants to argue they agreed to everything Rhaegar did – would be ready and willing to risk their families for it, solely on Rhaegar’s word. But, as the main novels prove, it’s a rare person who would give credence to what sounds like fable and old wives’ tales without a shred of evidence. Despite its actual accuracy, the prophecy isn’t an easy thing to believe – see the reaction of everyone who hears about the Others without actually seeing them in canon for reference, from Tyrion to Bowen March (and that’s when there is eyewitnesses to the dead rising). See the reaction to Daemon the Dreamer in the Mystery Knight, or to Jojen’s dreams in Winterfell for an idea of the common response to prophetic dreaming. No one believes the stories until they see the Others with their own eyes. Some, like March, even go to great lengths to deny the testimonies of those who saw them because believing that they are lying is easier than believing that mystical beings that raise the dead are attacking Westeros. The more likely reaction to the prophecy from anyone is disbelief, with the possible exception of the Targaryens because belief in prophecy is a very intimate and almost natural thing to a dynasty that survived because of a dreamer. But there were still skeptics within the Targaryens; Daeron the Drunken’s prophetic dreams certainly don’t seem to have been given much credence or understanding by his father Maekar, and it does not seem like Bittersteel put any stock in Daemon the Dreamer’s predictions of a dragon hatching at Whitewalls.

As far as the Starks go, while we don’t have anything specific that denotes how they might have received the prophecy, it bears mentioning that Ned dismissed Catelyn’s fears of “darker things beyond the Wall” as inspired by crib tales, and said that the Others and the Children of the Forest died eight thousand years ago. Maester Luwin even thought they never existed at all. Considering that any knowledge Lyanna had of the Others, like Ned’s, would have come from Old Nan’s stories, and that Maester Walys – a Reachman and son to one of the archmaesters of the Citadel – is no more likely to have believed that the Others existed than Maester Luwin, I think Lyanna was more likely to share Ned’s view than Rhaegar’s. Bear in mind that she grew up listening to tales of the Others as scary stories from Old Nan so her association of the prophecy is more likely to be “those silly stories from my ancient caregiver that she told to entertain and scare us” than “oh god, there is an ice zombie apocalypse coming and I have to have a child to stop it”.

Two, this argument ignores recent history as a strong incentive for anyone not to believe the prophecy. The birth of the prophetic saviors is tied to the return of the dragons, and everyone knows what happened the last time a Targaryen chased dragons: Summerhall.

The Targaryens had tried to bring dragons back for over a century to no avail to the point where tales of dragons in Essos were dismissed by almost everyone in current time as crazy tales. The most recent try had almost wiped out the Targaryen dynasty completely while they chased what sounded like pipe dreams and fanciful destinies. That’s not something that inspires faith or trust in any Targaryen who starts talking about dragons and saviors and three heads of the dragon, or their mental capability.

Three, this just waves away Lyanna’s personality completely as this inconsequential thing that won’t shape her response to the thought of having to do something. Lyanna Stark was not dutiful. She was not one to acquiesce to something simply because it was expected of her or it was her duty regardless of any other consideration. She’d be more likely to rail against it actually, especially in a scenario where her very wellbeing would be at risk. She was also 14 years old. What 14-year-old thinks it’s a good idea to be a vessel for a savior? What 14-year-old thinks it acceptable to be carried as far away from her family as she could get just so she could be impregnated with a prophecy child? And based on what, Rhaegar’s word?

Four, even if I accept that Lyanna did believe in the prophecy, the idea that it somehow absolves Rhaegar is a myth. It does not change the political calamity he caused by vanishing with Lyanna for months. It does not change his willingness to kill Lyanna’s own brother to retain the throne or his fighting in his father’s name. It does not change the fact that Rhaegar was the adult in this situation, an adult who knew fully well that Lyanna’s pregnancy at her age was high risk but left her in a desolate tower in the care of three Kingsguard instead of providing proper medical care. It does not change Lyanna’s young age and how susceptible it made her to pressure from Rhaegar, not made at all better by the inherent power imbalance in the relationship, which was only compounded by Lyanna’s isolation and complete dependence on Rhaegar and his Kingsguard at the Tower of Joy. It does not change that there was literally no reason for Rhaegar’s haste in acquiring the third head of the dragon, or for choosing the stupidest and most callous way to accomplish it. 

Rhaegar’s actions don’t cease to have consequences if Lyanna believed in the prophecy. His accountability and complicity in instigating the rebellion do not get erased if Lyanna believed in the prophecy. Rhaegar had a responsibility to Lyanna, her baby and the realm (not to mention Elia and her children), and he squandered it. He should have known better. He should have done better.

Five, any love Lyanna might or might not have felt for Rhaegar, any belief she might or might not have had in the prophecy promptly goes up in smoke the minute she learns about Rickard and Brandon, and Rhaegar decides to declare for the man who killed them and go fight Ned. That loses Rhaegar any credibility or any trust Lyanna had in him. I don’t believe that Lyanna would ever think the lives of her family are worth sacrificing ~for the greater good~. We’ve seen Stannis Baratheon, a grown man and a hardened battle commander, struggle with that very same notion, but Lyanna, at most 15 at the time and attached to her family as she was, should accept it on the word of the man who probably assured her that things would be alright, only for Lyanna’s family to get brutally murdered as a result? That’s too unbelievable for me.

I also have to ask: why should Lyanna accept that greater good argument when it’s her family that payed the price while Rhaegar demonstrated absolute refusal to pay for anything he’s done or even compromise? If sacrifice is expected–needed even– why did Rhaegar refuse any risk to his throne, even if retaining the throne came at the cost of Ned’s life?