It is a common misconception though, perhaps bolstered by anecdotal experiences where the two drugs were confused. Larger doses of K can incapacitate you, so it's not totally off base to think it could be used in that way, but it's certainly not why it's banned by the DEA. It's banned bc of the drug war military-industrial complex.
Science might be finally gaining the upper hand in the drug war against political forces which won the public opinion battle back in the 70s. It's much harder to convince the public drugs r bad if 95% of the "hard" drugs have medical uses.
Virtually any sedative can be a "date rape drug". As that page notes, very-much-legal alcohol "is the drug most commonly used to help commit sexual assault".
Ketamine has substantial legitimate medical uses, and is thus legal in those situations.