I found the terms for solving this difficulty through numerous readings and teachings of the late tragedies of Shakespeare, and by chance in a would-be offhand comment in an otherwise perfectly obscure letter written by the 20th century Reformed Protestant theologian Karl Barth.
One of the qualities of Shakespeare’s characters – in this case, his villains – I most admire is that they are intelligent. Shakespeare gives them brains and, more important, he lets them use their brains. This corresponds to the fact that not only do they know what they are doing and why, but that what they are doing is in fact malevolent or evil. Some of the characters have no conscience whatsoever, bad or otherwise. But some – the most interesting and complex and irreducible, I’d say – do have consciences and Shakespeare gives generous amounts of time and space in his plays to allow those characters to wrestle with them.
Macbeth knows what the consequences of murdering the king, Duncan, will eventually lead to from the instant he begins plotting to do so. Much of the play depicts Macbeth’s descent into blood-steeped insanity through his efforts to suppress his clear and rational knowledge of those consequences, abetted by Lady Macbeth whose continual cajoling amounts to telling him to stop all his reasoning, in effect, to stop thinking. Claudius, in Hamlet, has a remarkable soliloquy in which he lucidly and with great eloquence parses the reasons why his prayers to be pardoned for murdering his own brother will not be granted, as he still enjoys the wicked fruits of the act, namely the crown and his brother’s widow.
Macbeth, Claudius, and many other characters in Shakespeare dramatise something that, if anything can be reasonably called so, is a universal human experience – knowing what’s right yet acting wrongly anyway. Knowing better than how one acts or feels is observable at every scale of human experience, from knowing you should not have that second piece of chocolate cake but eating it anyway, to knowing cigarettes are lethal to your health but having a smoke anyway, to knowing you should not leave your battered neighbour to perish in a roadside ditch but hurrying past them nevertheless. I knew from early on in the process of writing This Other Eden that, whatever I discovered about Matthew Diamond and his relationship to the characters on Apple Island, I had to allow him to know all of it as well, no matter how mixed or undiluted his sentiments and motives, and I had to allow him the time and space in the story to wrestle with his best and worst impulses.