Despite what the numerous Kant jokes would lead you to believe, deontology is persuasive. It was my favorite normative philosophy when I was in college, probably motivated at least in part by my conservative religious upbringing. Perhaps more persuasively, in a large survey of 700+ professional philosophers, around 1/3 of them (32%) at least leaned towards deontology. It was narrowly beaten out at 37% by virtue ethics (really??); consequentialism came in third with 31%.
Part of the appeal is the seeming simplicity: deotologists don't need to predict in complex detail the implications of their action, but rather just act in accordance with universalizable maxims. Is it ok to go to war and kill an enemy combatant? Well It's Wrong because if that maxim were universalized, everyone would be justified in killing in any war. So don't do it (says the deontologist). Is this lie or that lie wrong to tell? Lying Is Wrong so don't do it (says the deontologist).
The oft-cited knock-down argument against this is the Inquiring Murderer problem. You're in your house when a friend rushes to the door and tells you she needs to hide, there's a murderer after her. So you hide her, and a few minutes later a crazed man with an axe comes knocking, and asks you if you've seen the friend. If you tell him that you haven't seen her, you are confident the murderer will leave and go search elsewhere. Is it ok to lie then? (This was Kant's own example, by the way, not some gotcha by a critic; Kant readily bit the bullet and said no, you mustn't lie.)
Most people disagree with Kant on this example (at least from what I've gathered), and that goes for me as well. But there's something weird about the setup of the question. You have done nothing to put yourself in this situation, you sitting alone in your house. Your friend came to your door for help. More importantly, the axe murderer came to you. It would have been so easy to be moral if you didn't have crazy axe murderers at your door all the time!
To really give Kant his due, I think we need to recognize that in his imagined ideal world, where everyone abides by the univeralizable maxim (his Categorical Imperative), would actually be pretty great. At least, I think it would be a far better world than the one we actually find ourselves in. You wouldn't need to worry about killing in war because nobody would go to war for fear of violating the CI. You wouldn't need to lie to axe murderers because they would go get counseling instead of chasing your friend and putting you in an uncomfortable situation. You might feel uncomfortable when your friend asks you if their shirt makes them look fat and you can't tell a lie, but there are good reasons to think this is an improvement too.
Kant's Kingdom of Ends actually sounds like a pretty great place to me.
The problem is, we can't get there from here. On Sam Harris' proverbial Moral Landscape, the goal is to be on the highest hill you can possibly reach, but hills and valleys stretch out nearly to infinity. Even if you think we are a beautiful hilltop--many would disagree and argue we are trapped in a valley--but if you believe this, in order to reach anything higher we may have to traverse some valleys. The Kingdom of Ends may be too far to even see, from where we are today.
Maybe we're lucky and we find a stretch that only ascends; that's Easy Mode morality, where all you need to do it keep walking the path. But sometimes the path to a better world lies across the ravine. That means climbing down for a while. That means doing something that's actually bad, keeping your eyes wide open and fixated on the highest peak you can see, because this is the best way to get there.
"If you want to make an omelette, you're going to have to break a few eggs."
This, I posit, is the double-edged sword of ideology. Ideology leads you to pursue the highest peak in the moral landscape, but in doing so, drives you into the ravine. Some make it to the other side; others never climb out.
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I always see movies about politicians with bright eyes and big dreams of changing the system, only to have it change them instead. One explanation is that everyone is corrupt and selfish deep down, and if you put them in the wrong circumstance they will expose themselves for who they really are. Maybe. But a more charitable interpretation is that politics selects for ideologues. They see a beautiful Possible World in front of them, just on the other side of a deep chasm of corruption and shortcuts and dirty deals. And what's more, they think they can do it, they can carry everyone on their back up the hill to the promised land. If they just play the game, do the time, make the deals (corrupt or not), they will be able to climb out in the future. And I guess most don't succeed, and the wheel keeps turning.
And what should they do instead? Not try to change a dirty, corrupt system? Kant says: Not if you need to do bad things to get there. But then, how do we get there?
What all of this analogy fails to acknowledge (maybe Sam talks about it in his book, I honestly don't remember) is that we are all in some sense on our own moral landscape, which is coupled to but not identical to others'. And when others fail, they take us down with them, to greater or lesser extent. Our own ground becomes shifting sand and we have to adjust and change along with the circumstance.
(There is, of course, a sort of Meta-Moral Landscape that encompasses the totality of all the individual landscapes we all occupy... but that's not where you live!)
When the axe murderer it at your door, there is no way to simply hold your ground and stick with your principles. All directions are down. If you honor your principle to Not Lie, you fail your principle to Protect Your Friends, and vice versa. This circumstance is not your fault. But you still get to decide, and you need to own that decision and deal with the repercussions fully.
My own silly version of morality is to always Do Your Best. In the landscape analogy, it more or less means to always ascend, never descend. When the ground shifts under your feet, when the axe murderer is at your door, you have to make a choice, and you should make every effort to make the best one. And whether you succeed or not in that moment, you must do the same the next day, the next hour, the next minute. Your actions determine your future landscape, at least in part, and in each action, you can choose to climb up or down.
Jordan Peterson likes to say: If you can't make the world better, at least make sure you're not making it worse. This seems pretty spot-on.
In Kant's view, we are to keep our feet firmly planted on the spot where the possible Kingdom of Ends could eventually be, and hope everyone joins us.
In the Ideologue's view, we are to trot like soldiers in as straight a line as possible to the highest peak we can see, regardless of the terrain.
I say, you have a duty to see your own terrain as clearly as possible, but at the end of the day no-one can make your choices for you. Of course, others can help you understand your own situation from other points of view, and you can help them in turn. But your best is not their best is not your best yesterday or your best tomorrow.
As I've said many times, Doing Your Best includes learning how to make your best better. This includes, of course, learning about normative ethics and effective altruism and all the other excellent resources for deciding which way to step. At the end of the day, there is a right answer about which way you should have stepped, though you may or may not know what it is when you make that decision. That's ok too; do better next time.