That it was mercy to kill them, or at least an acceptable collateral damage. Graendal would not have let Rand get anywhere near her and it is certain that everyone in that palace, even the high number of Darkfriends, had a level of compulsion on them that would have incurable and even led to them sacrificing themselves in order to achieve Graendal's escape.

Those people, IMO, were dead anyway. Rand was also considering he price of letting Graendal continue to manipulate Arad Doman.

For me, the worst atrocity in the series was the state that Graendal left Arad Doman in. The scene with Rand leaving them totally helpless turned my stomach - there was nothing more to do.

The irony is that the Domani believed the Dark One to be dead.