a fundamentalist Christian, who asserted that he only behaved "morally" because he feared God, and that anyone who, not believing in God, behaved "morally" was insane. That behaving decently to fellow human beings for no other reason than it might encourage them to be decent in return was a nonsense. The only concept of free will he understood was you decide to obey God, or not - and as a consequence, are damned.
Kant's categorical imperative gives as good a formulation as any for a workable G_dless ethics:
Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end.
A sense of morality solely based on fear and obeying the orders of a supreme being
is reactionary (both in its political sense and in the sense of reacting to a stimulus). "Today I think", says G_d, "it is immoral to wear Dunlop Green Flash and drive an SUV. Cast such people from your communities."
Cue worried parsing of the sentence:
"Look I drive an SUV but I don't wear Green Flash. I'm not immoral. Phew".