Deceit in the cases under discussion here is mostly in the eye of the beholder. If a poem is 95% identical to someone else's, as it apparently is in some cases, then I can see the argument that they're pretending to have written things they didn't write. At that point it is cynically slapping one's own name on someone else's poem. There's no artistry to be had in what they did. So I just shrug. I still can't get outraged over it.
More importantly, that's not really what's going on here for the most part I think. For many of these poets being given a dose of Lightman's paroxysmal spleen, there's no earthly reason to think they intended to do anything other, or more, than
what Quevedo did when he lifted a third of a sonnet or so from Du Bellay in writing his own. Or what Du Bellay did when he, in composing that sonnet, lifted most of it from a relatively obscure Latin poem by Janus Vitalis. (In neither case was citation given.)
Don McKay above took somebody else's poem and produced a much worse poem with his alterations.
But what would we say if the end result had been a better poem, as with DesRuisseaux I think it sometimes is?
One can justifiably argue that particularly with DesRuisseaux's work — particularly the part cited in the article — the original was indeed being "recontextualized or reimagined." If a French-language poet inserting a heavily altered (and translated) stanza from a poem in another language into their own work is a plagiarist, then I submit that that word has been redefined to the point of uselessness. I am unable to find the actual French poem, and don't know how long it is or what else it contained. But the case as presented in the article makes me go "oh please, don't you have actual important things to do?"
I won't insult anyone here by assuming that they don't realize that good poets even today in English do this kind of thing. Not just as mere quotation but because they happen to like the phrase or the motif, or wanted to play with a given passage by someone else and see what came of it. The temptation to do it is particularly great if the text being appropriated is in another language. It is omnipresent if — like a great many 19th century Russian poets — you do a lot of your pleasure reading in languages other than the one you write in.
When it happens, the poets don't usually give credit. (Though I myself actually do. Or at least try to, when the editor will allow it.) I think the only major poet who made a habit of this and was truly scrupulous about "citing his sources" is Donald Justice. And I just don't buy that, if Donald Justice hadn't cited, he would have been guilty of unpardonable deception of his readership against the public interest. (Though that would have made it unfortunately harder to enjoy comparing Justice with his sources side-by-side to see how Justice conducted himself in dialogue.)
But since you raise the point, no I don't really think that deceit by itself on the part of an artist — even intentional deceit — is worth getting that moralistically bent out of shape over, unless it does some appreciable amount of harm to real human beings or their property or the public interest. Till someone is stiffed out of large amounts of money in some way as a result of undetected textual appropriation, I still don't really care. (Maybe it has happened and I'm unaware.) DesRuisseaux's fame in no way hinges on the accomplishments of Dylan Thomas or Maya Angelou or others. (For one, he wrote much better than Maya Angelou.) It's true that some of his work involved uncredited reworking of poetry from another language. A trait it shares with a considerable proportion of Ezra Pound's Cantos, and most of Ivan Krylov's fables.
Moving on.
Even at worst — in the cases of 95%-verbatim lifting — this kind of thing seems no more than an artistic misdemeanor. It probably isn't hurting the original artist's book sales any — if sales they have. Maybe I'm wrong but an artist getting undeserved, or rather misdirected, acclaim via 95%-verbatim theft probably doesn't normally cause the original artist any great injury except in unusual cases or where the public lacks access to the original. It isn't a moral issue as far as I can see, so much as one of tact. Not unless one has a pathological fear of the possibility that somebody somewhere may be getting more than they deserve.
Sort of tangential but: Deceit may also part of the artistic toolkit, a way to push boundaries, or to protect them. We all know now that the Sonnets from the Portuguese weren't really from the Portuguese. See also
this article on a forged trobairitz. And half the time when Borges opened his mouth in front of an audience he was telling something other than the full truth — with them often being none the wiser.