And how many times did he escape after that? And how many people died as a result?

THIS!
Frosstbyte nails it!

And frankly, any evidence he collected would be hearsay anyways. Who would be able to testify as a witness with personal knowledge of where the evidence came from?

Except that she didn't believe that there was any way that Kilgrave could be stopped or held. She'd already tried it and failed. Somehow, he'd always escape and then kill and traumatize others. This was the only way she knew to stop him and protect everyone else on the planet — and specifically Trish, who he'd JUST…

All of this is valid. But I also think that Jessica truly believes that there is no way that the world is safe as long as he is alive. Somehow, he will manage to escape and abuse and enslave and traumatize more people.

It gave us the notion that there may be a whole group of Moriartys that Sherlock will now have to deal with. That's HUGE.

But we didn't know for sure. And more to the point, this introduces the notion that there are other Moriartys out there. That's a major step forward for this series.

I'm still not sure what I think of the scene. But one point of clarification: I just re-watched the scene because I had missed her holding Joffrey's hand. And I didn't miss it. She never did. It was crossed over his chest the whole time. There are several points in the scene where we see both of her hands. And…