[Kelson shook his head.] It was never a secret. But when the Festil's were overthrown and my ancestors restored, humans forgot that not all Deryni were responsible for their crimes. People have short memories.

2/3 of the population were killed, most went into hiding.

I guess you could say the nonmagical world had enough. Combine it with anti-magic religious rhetoric and Gwynedd was ripe for anti-magic backlash.

[He looked at Quentin for a moment.] I should be preaching tolerance and unity but if separation is working for you, don't let fail. The price for peoples lives is too high.