Not all of them
Only the forced ones
Those who were forced were most likely killed in the process, but those who already became knights are likely to have been willing （￣へ￣）cuz those Saint bullshits do not come off as people who have been forced to willingly kill and do atrocious stuff to innocent people.(〜￣△￣)〜 I bet they even enjoy killing people.
Saints aside, I don’t think the knights are completely willingly, it was clearly shown how Dory and Borg became knights also that girl let’s call her Brooks daughter remembered a memory which means she’s not fully dead and Imu didn’t give her a chance he completely brainwashed her!
Really Oda!