Assume a person was present when his or her best friend died in a horrific manner. Slowly fed into a woodchipper after weeks of torture. You get where Im going here.
Is lying about their mode of death, and instead telling their loved ones they died peacefully and heroically (and holding that secret to your grave) to give comfort to their loved ones (and holding that burden yourself) an act of evil?
Who (other than yourself) are you harming?
I appreciate that that's what you're going for, but that's
explicitly not how very very hard deontology interprets things. Naturally you--and I, and many other people besides!--do not really share this view. (I'm mostly a virtue ethics guy personally; Philippa Foot is one of my philosophy heroes.)
That is, this is a bit like being a physicist going to an electrical engineers' conference and getting upset that they use "j" to denote the imaginary unit rather than "i." You are, essentially, saying "the deontologist MUST only work with
my definitions and no others," which the deontologist is just as free to balk at as you are to balk at their rather strident insistence about the alleged "harm" caused by lying to others. Again, I have no skin in that particular game, because I am not a deontologist to begin with, but you should know whenever you get into a debate about ethics that "when I say 'harm,' I specifically mean grievous
physical harm and nothing abstract or philosophical" is
not going to be met with a particularly friendly response.
(Again, for my own position, the various virtues--and their corresponding vices of excess and deficiency--encapsulate why telling the truth is morally superior as a general rule, but make allowance for deceiving a person whose aims are bad. However...)
I personally disagree, and so does DnDs implicit morality.
I'm not sure you do. I mean, I can't read your mind, so perhaps you disagree, but "the truth is preferable to falsehood in general" is a pretty common ground rule of moral behavior. E.g. the ethic of reciprocity rejects telling lies in both its positive and negative forms. "Do not do unto others what you would not have them do unto you" (the negative version of the ethic of reciprocity, sometimes called "the silver rule") would imply that, since we do not want others to gain advantage over us or manipulate us via lies, we should not tell lies to others. "Do unto others as you would have them do unto you" (the positive ethic of reciprocity/"golden rule"), which unlike the previous version
requires actions instead of merely
forbidding actions, expects of you that you tell the truth to others if you wish for others to tell you the truth.
These aren't complex philosophical theories; these are simple moral maxims everyday people use and live by. I would be
extremely surprised if you said that lying about any random thing whenever a person felt like it was an acceptable behavior, for example, even if the harm caused by those lies failed to meet your "thrown into a woodchipper" standard. E.g., if I lie to someone to tell them I am vaccinated for COVID when I am not, and they catch COVID as a result but experience only mild symptoms, I certainly haven't done any harm to them that is comparable to throwing them in a woodchipper, but I suspect you would consider me morally at fault for having told that lie. (Please do tell me if you WOULDN'T think that though! That implies a very interesting discussion/explanation!)