GRACE: This is your 'Just one trip'? You take me someplace with an excruciating moral dilemma?

DOCTOR: Not every place I go is as pleasant as San Fransisco, Grace.

OREN: How could they have done such a thing, Doctor?

DOCTOR: Fear can drive the mind to accept the most hideous prospects. Fear of death, of extinction. It can overrule mercy, reason, even sanity, if you allow it.