5
" Loving, of enemies is another dogma of feigned morality, and has besides no meaning. It is incumbent on man, as a moralist, that he does not revenge an injury; and it is equally as good in a political sense, for there is no end to retaliation; each retaliates on the other, and calls it justice: but to love in proportion to the injury, if it could be done, would be to offer a premium for a crime. Besides, the word enemies is too vague and general to be used in a moral maxim, which ought always to be clear and defined, like a proverb. If a man be the enemy of another from mistake and prejudice, as in the case of religious opinions, and sometimes in politics, that man is different to an enemy at heart with a criminal intention; and it is incumbent upon us, and it contributes also to our own tranquillity, that we put the best construction upon a thing that it will bear. But even this erroneous motive in him makes no motive for love on the other part; and to say that we can love voluntarily, and without a motive, is morally and physically impossible.
Morality is injured by prescribing to it duties that, in the first place, are impossible to be performed, and if they could be would be productive of evil; or, as before said, be premiums for crime. The maxim of doing as we would be done unto does not include this strange doctrine of loving enemies; for no man expects to be loved himself for his crime or for his enmity.
Those who preach this doctrine of loving their enemies, are in general the greatest persecutors, and they act consistently by so doing; for the doctrine is hypocritical, and it is natural that hypocrisy should act the reverse of what it preaches. For my own part, I disown the doctrine, and consider it as a feigned or fabulous morality; yet the man does not exist that can say I have persecuted him, or any man, or any set of men, either in the American Revolution, or in the French Revolution; or that I have, in any case, returned evil for evil. "
― Thomas Paine , The Age of Reason
10
" If now we attend to ourselves on occasion of any transgression of duty, we shall find that we in fact do not will that our maxim should be universal law, for that is impossible for us; on the contrary, we will that the opposite should remain a universal law, only we assume the liberty of making an exception in our own favor or (just for this time only) in favor of our inclination. Consequently, if we considered all cases from one and the same point of view, namely, that of reason, we should find a contradiction in our own will, namely, that a certain principle should be objectively necessary as a universal law, and yet subjectively should not be universal, but admit of exceptions. As, however, we at one moment regard our action from the point of view of a will wholly conformed to reason, and then again look at the same action from the point of view of a will affected by inclination, there is not really any contradiction, but an antagonism of inclination to the precept of reason, whereby the universality of the principle is changed into mere generality, so that the practical principle of reason shall meet the maxim half way. Now, although this cannot be justified in our own impartial judgement, yet it proves that we do really recognize the validity of the categorical imperative and (with all respect for it) only allow ourselves a few exceptions which we think unimportant and forced from us. "
― Immanuel Kant , Groundwork of the Metaphysics of Morals
13
" [A man] finds himself forced by necessity to borrow money. He knows that he will not be able to repay it, but sees also that nothing will be lent to him unless he promises stoutly to repay it in definite time. He desires to make this promise, but he has still so much conscience as to ask himself: Is it not unlawful and inconsistent with duty to get out of a difficulty in this way? Suppose, however, that he resolves to do so, then the maxim of his action would be expressed thus: When I think myself in want of money, I will borrow money and promise to repay it, although I know that I never can do so. Now this principle of self-love or of one's own advantage may perhaps be consistent with my whole future welfare; but the question now is, Is it right? I change then the suggestion of self-love into a universal law, and state the question thus: How would it be if my maxim were a universal law? Then I see at once that it could never hold as a universal law of nature, but would necessarily contradict itself. For supposing it to be a universal law that everyone when he thinks himself in a difficulty should be able to promise whatever he pleases, with the purpose of not keeping his promise, the promise itself would become impossible, as well as the end that one might have in view in it, since no one would consider that anything was promised to him, but would ridicule all such statements as vain pretenses. "
― Immanuel Kant , Groundwork of the Metaphysics of Morals