Daenerys obviously enjoyed his suggestion at first. She wanted nothing more than to unleash her rage upon something, anything. The Freys were indeed the ideal option; hated by the North, untrustworthy to her regime.

...but was it truly just?

"...will there not be those who accuse me of striking down the Freys because they would oppose me? Would they not accuse me of silencing all those who would speak out against me? Would they not call me a tyrant?"

There was a long pause before she spoke again. "Would they not call me 'Mad'?"