Equating Karaims to MO clearly comes from someone who met neither, but listened to some speaker.
Karaims were also different from individuals violating something: they were centuries-old communities that followed their tradition. Maybe modern Reform is a better comparison, as they follow generations of their leaders. I had once a reform person helping me out with a ride during the summer trying to make sure I’ll be at the destination by 5pm as he thought that shabbat starts 5pm sharp every week they way they celebrate at his temple – and he was intent that I don’t violate it. Glad we cleared it on the way, or he’d get a speeding ticket.
Also, are Karaims mehalel shabbos miduaraita? I picture them sitting in the dark, eating cold pizza without their wives. Weird, yes, but what malochos do they perform in the process?