siren: any of a group of female and partly human creatures in Greek mythology that lured mariners to destruction by their singing.
As a whole the sentence is saying that when we don't want to face reality, we are willing to be led astray by something more pleasant, even if that is exactly what we should not do because it will turn out quite unpleasant after all.
Or shorter: If we don't want to see that we're being conned, we'll let ourselves be conned.