I've heard about police using ketamine on arrestees to subdue them (often leading to serious health complications or death), but never non-LEO criminals. Found one news story where victim claims drug was ketamine, but seems there was just one big story, not many.

What is the scenario that concerns you?

I think ketamine's dosage (100s of mgs) and oral activity (low) is not conducive towards secretly drugging someone. To drug someone with ketamine without their consent, you'd likely have to inject them. If someone is injecting a victim with a drug to knock them out, ketamine seems like it'd be a lot safer than heroin and somewhat safer than benzos - both of which would have a higher chance of respiratory depression.

I suspect this "long history" is drug war propaganda - ketamine would be more expensive and less convenient than other similar options for incapacitating someone via injection.

If it's being used as a weapon, that sounds like it should be protected under the second amendment.

I imagine guns and knives are the most popular choices for subduing kidnapping victims, and they're explicitly legal because they can be used in that way

They meant as an ongoing way of controlling the kidnapee in a more cooperative state not the initial gun to the head "come with me, we're kidnapping you"