> Defectors are notoriously unreliable: they tell their host country whatever they want to hear

This is almost word-for-word the same rationalization employed by the people who denied the Cambodian genocide.

Maybe, but unfortunately it cannot be used as a strike against it.

The Cambodian genocide happened.

Defectors are notoriously unreliable and many Soviet defectors told falsehoods their host country wanted to believe. (This doesn't mean every defector is unreliable, or even that everything an unreliable defector will say is false -- it just means what it means, that defectors are unreliable as a category.)

Both things are true.

Sometimes defectors are unreliable. Other times, defectors can provide otherwise unavailable information which people choose to dismiss or ignore because it doesn't fit with their presuppositions.