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With this context of the gang member asking Matthew to keep Jin from fighting I can understand why he used the sedative to keep Jin there for 4 days.
Jin would have immediately thrown himself back into that mess as soon as he was coherent and they are all afraid he'd end up dead if he kept doing that so I kinda get Matthew's drastic actions.
Still, you should never drug your partner (even if you believe it's to save them) so Jin's mistrust of Matthew is valid as he did betray his trust. Matthew should have come up with a better way to keep Jin out of the gang war is all.