Given the discussion that Morgan and Duncan have with Cardiel (in TBH, I think?) about the ethical considerations involved in tampering with people's minds and memory, and the fact that Kelson's ethical thinking would've been highly shaped by Morgan, at the very least, and that Duncan's his confessor, my guess is that Kelson only sets controls in his squires because they're sometimes required to be present when Kelson has to discuss highly confidential state secrets and/or dangerous and potentially deadly (given the prejudice of the times) Deryni secrets. He'd probably consider the controls to be necessary not only to protect the secrets themselves, but also to protect the squires. After all, what they don't remember, they can't be forced to divulge to others, whether they be hostile bishops such as Loris, or hostile Deryni such as Charissa. True, it would be better if he could ask for consent first, but when one of those secrets happens to be "The King has powers that are more Deryni-like than even the average empowered Haldane before him," well, it might be harder to broach the topic of consent with a human squire who might have reservations about serving a half-Deryni King. One would think that such a squire wouldn't be serving in the Haldane Court in the first place, but then again, do young boys really have much of a choice when they're tapped for the King's service? So it would be possible for someone to rise in the page/squire ranks on merit, I'd think, and then get to the point of being so good they're picked to be in Kelson's personal service...and if they balk then once they find out some of his secrets, and decide this wasn't what they signed on for, that would be a major security breach. So I can see why Kelson might think this is a case of "It's easier to ask for forgiveness rather than permission."