If Aemon failed to save Aegon, history might lose a pretty song but wouldn't it be better for everyone else? Daemon gets Blackfyre & no deathbed legitimatization could that be enough to sway a Rebellion? Aemon vs Daemon!
Yeah, it’s a reasonable question. Aegon the Unworthy made the world aworse place while lived; Aemon the Dragonknight seems to havemade it a better one. But there is a concrete principle here asidefrom honor. If the kingsguard picks and chooses which kings they’reactually going to protect,then you have a system where security forces are effectivelyselecting the head of state, and nobody wants that.
It’s less of an issue in the main series because the kingsguardis in such bad shape overall, but that question of trust in thekingsguard is a live one throughout the Targaryen dynasty. Fireballturned traitor when he didn’t get the kingsguard appointment hewanted, which probably demonstrates why he wasn’t appointed to thekingsguard. Aegon IV really was a bloody-handed tyrant, but whathappens when the social class which produces most of the kingsguarddecides that Aegon V is a “bloody-handed tyrant”? Egg filled uphis kingsguard with commoners and (probably) bastards because he cared about meritocracy – but probably alsobecause they’re less likely to kill him in his sleep for caringabout meritocracy.
Given what we know of the facts here, this is a different questionthan Barristan’s regrets about having saved Aerys at Duskendale.That feat was something nobody but him could have done, and thus,that nobody would have expected him to do. If he hadn’tsuccessfully attempted it, it wouldn’t have drawn questions aboutthe kingsguard as an institution. The famous Dragonknight gettingdistracted by a butterfly during a public attack on the king is a lotsketchier. It’s more like the problem of Tywin’s defense of theRed Wedding: stop one unscrupulous tyrant now, allow the kingsguarditself to become an institution of unscrupulous tyrants later.
Now, if he could ensure a successful cover-up,there’s a reasonable argument that Aegon IV really was bad enoughto make this a fair question.
(That said, it might be the best piece of evidence against the“Daeron Falseborn” story, not because of what it says about hishonor, but because you’d expect a more calculated response fromsomeone with the sangfroid to undermine the monarchy like this for 25+years. Ned’s story about his snephew wasn’t half as bad as that,and look how nuts it made him in a few months at court.)