Some of the most effective intelligence agencies in history have served the most odious dictatorships. The Soviet KGB, the East German Stasi, Cuban state security — many American intelligence pros ruefully concede that these services ran rings around Western counterparts, even if some of the regimes they served eventually collapsed anyway.
This is no accident. One-party states, as that descriptor implies, combine a certain unity of purpose with total insulation from democratic accountability. This gives their secret agents latitude to get the job done, through extortion, infiltration, assassination — whatever it takes.
In a multiparty democracy, by contrast, such methods go against the political grain. The government may resort to them, but its mandate is a bit tentative. The government depends, crucially, on an underlying, voluntary political consensus strong enough to support the inevitable moral trade-offs.