“There are bad people in this world who are motivated by hate.”

Although very commonly attributed to Fields, this is derived from a statement that was actually first said about him by Leo Rosten during a "roast" at the Masquer's Club in Hollywood in 1939, as Rosten explains in his book, The Power of Positive Nonsense (1977) "The only thing I can say about W. C. Fields ... is this: Any man who hates dogs and babies can't be all bad."
Misattributed
Variant: Anyone who hates babies and dogs can't be all bad.

Although a very common misconception is to attribute the final part of this quote to W.C. Fields himself, it was actually first said about him by Rosten during a "roast" of Fields at the Masquer's Club in Hollywood in 1939, as Rosten explains in his book, The Power of Positive Nonsense (1977).
Context: The only thing I can say about W. C. Fields … is this: Any man who hates dogs and babies can't be all bad.

On Coalition Government (1945)

The True Believer (1951), Part Three: United Action and Self-Sacrifice
Context: It is easier to hate an enemy with much good in him than one who is all bad. We cannot hate those we despise. The Japanese had an advantage over us in that they admired us more than we admired them. They could hate us more fervently than we could hate them. The Americans are poor haters in international affairs because of their innate feeling of superiority over all foreigners. An American's hatred for a fellow American (for Hoover or Roosevelt) is far more virulent than any antipathy he can work up against foreigners. It is of interest that the backward South shows more xenophobia than the rest of the country. Should Americans begin to hate foreigners wholeheartedly, it will be an indication that they have lost confidence in their own way of life. <!-- p. 96

page 267
Born a Crime

Source: The Love Dare

È uno de' vantaggi di questo mondo, quello di poter odiare ed esser odiati, senza conoscersi.
Source: The Betrothed (1827; 1842), Ch. 4, p. 44