Does this fan theory explain what happened with Game of Thrones’ ‘Tower of Joy’ flashback?

There's so much we're still trying to get our heads around after the thrilling climax of Game of Thrones season six.

But one of the things is the bombshell about Jon Snow's actual parentage which blew the old 'Ned Stark's bastard' yarn out of the water. The denouement of the explosive sixth series confirmed the 'R+L=J Theory' that Snow is in fact part Targaryen, the son of Rhaegar Targaryen and Lyanna Stark (Ned's sister). Yet as gobsmacked fans were left trying to compute the ramifications of this news - still unbeknown to Jon Snow as of yet - for season seven with Daenerys Targaryen heading with her armada and dragons to Westeros. But eagle-eyed fans were left puzzled by the flashback scene at The Tower of Joy which threw up the true nature of Snow's lineage. One Reddit user called Therapy in particular wondered why the hell Rhaegar Targaryen ordered his top swordsman Ser Arthur Dayne to guard Lyanna from her brother instead of sending him to fight against Robert Baratheon and his army.

A few things about the Tower of Joy scene puzzled me: Why is there any fighting at all? Ned is Lyanna's sister and can be trusted with her and her baby. Before fighting, Arthur Dayne tells Ned, "Good luck in the wars to come," a strange thing to say to someone you are about to fight to the death with. When only Dayne and Ned are left, Dayne could easily kill Ned at any time (as the Three Eyed Raven said, he wasn't just better than Ned, but far better) - why delay?

Therapy's theory is that it's because Ser Arthur Dayne's commands were to leave Ned, and only Ned, alive. He reckons Rhaegar knew Ned could be trusted with Lyanna and the baby, while knowing the identity of baby Jon had to be kept secret. While Ned alone can keep a secret such as that, the other 5 men seeing Ned coming out of the tower with a baby massively increase the likelihood of the secret getting out, the post suggests. So therefore he believes the best course of action would be for Ned to return North with the infant Jon alone, with nobody knowing where he came from.

If true, then regarding the three puzzling points above, Fighting is necessary because Dayne can't just tell Ned, "Your men need to die in order for an important secret to be kept." Even after seeing Lyanna and promising her to keep the baby safe, Ned wouldn't have his men murdered - it's not in his nature. Therefore Dayne must kill them. Dayne knows Ned will survive the battle, since he won't kill him. Ned's life was never in peril. But Dayne doesn't know if he himself will survive (he's amazing, but you never know for sure). So he takes the opportunity to wish Ned luck, since he and Rhaegar honestly do hope he succeeds. I'm less sure of why Dayne keeps fighting after only Ned is left. I would guess that Dayne is trying to prove to Ned that he could easily kill him, for example, by disarming him and then sparing his life (which is harder than killing him and takes more time). Then Ned would believe what he tells him about his orders from Rhaegar, after which Dayne would "vanish", leaving Ned with Lyanna and the baby. Instead, Howland Reed wasn't actually dead, and he surprised Dayne, leading to his death. But Rhaegar's plan still worked, since Ned promised Lyanna to keep the baby safe, as expected, and while another person knew the secret, Reed could in fact be trusted with it.

Here is every scene about the intriguing tale in one handy video.