Those who mean well themselves think well of others by WILLIAM HAZLITT

Thus it has always been.Those who mean well themselves think well of others, and fall a prey to their security. That humanity and sincerity which dispose men to resist injustice and tyranny render them unfit to cope with the cunning and power of those who are opposed to them. The friends of liberty trust to the professions of others because they are themselves sincere, and endeavour to secure the public good with the least possible hurt to its enemies, who have no regard to anything but their own unprincipled ends, and stick at nothing to accomplish them.
WILLIAM HAZLITT, Characters of Shakespeare's Plays