The Christian determination to find the world ugly and bad has made the world ugly and bad.

[Der christliche Entschluss, die Welt hässlich und schlecht zu finden, hat die Welt hässlich und schlecht gemacht.]

Friedrich Nietzsche (1844-1900) German philosopher and poet

The Gay Science [Die fröhliche Wissenschaft], Book 3, § 130 (1882) [tr. Hill (2018)]
    (Source)

Also known as La Gaya Scienza, The Joyful Wisdom, or The Joyous Science.

(Source (German)). Alternate translations:

The Christian resolution to find the world ugly and bad, has made the world ugly and bad.
[tr. Common (1911)]

The Christian resolve to find the world ugly and bad, has made the world ugly and bad.
[tr. Kaufmann (1974)]

The Christian decision to find the world ugly and bad has made the world ugly and bad.
[tr. Nauckhoff (2001)]