"I feel obliged to say that the emotional universes that we inhabit are so distinct, and in deepest ways opposed, that nothing fruitful or sincere could ever emerge from association between us. I should like you to understand the intensity of this conviction on my part. It is not out of any attempt to be rude that I say this but because of all that I value in human experience and human achievement."
Bertrand Russell is unequivocal in his condemnation of fascism in a frank letter to Sir Oswald Mosley.
(Thanks to Adam for the link.)