And I'm retarded enough to keep my Alakazam in...
MetaGross66 said what I wanted to say - if you switch Alakazam out, then Mesprit's U-turn would buy his team momentum and therefore the advantage. If you keep Alakazam in, Mesprit KO'es. In either case Mesprit would then have turned a potentially deadly situation (Alakazam already in an threatening to attack) to an advantageous situation.
Furthermore, Modest LO Alakazam's Psychic does 34.2% - 40.5% to min/min Mesprit, so with some HP / SpD investment Mesprit can actually switch into Psychic + SR twice and threaten Alakazam out both times, assuming of course Alakazam doesn't predict Mesprit coming in and using Signal Beam / Shadow Ball. Scarf Mesprit looks very much like a counter to me.
@above - if Alakazam is scarfed it would also have to switch out, since it'd be stuck using Psychic on Mesprit ...























