Is there a reasonable defense of fidelity to your spouse that has a foundation that is neither legalistic or theistic? Is that defense superior to an alternate defense of infidelity? Can such a finding be placed on a base other than individualistic relativism?
My thought: if we accept that adultery is a kind of lying and that truthfulness is the core of morality, then adultery must on prima face grounds be immoral. There is also the distinction between doing something that you think is wrong (say adultery) and confessing that act to someone who may be harmed by that confession (say, your spouse and children).
And then the question becomes: what if your spouse acknowledges your adultery perhaps in the context of an "open marriage"? Is it then immoral? The main principle of Kantian ethics is that consequences needs to be divorced from the essence of the act itself -- that the essential rightness or wrongess of the actions must be weighed without regard to utilitarian, pragmatic, or perceived societal considerations. Thus, I think Kant would say that moral duty alone determines whether or not adultery is moral or not. OK, but is fidelity a moral duty, and if so, why?
What do you think -- are there reasons to say that adultery is immoral which don't depend on theistic or legalistic premises? Is it possible to defend marital fidelity from Kantian grounds, or is it even necessary to do so? Add your thoughts to the comments here or join the ongoing discussion in the forum.