Earlier quoted context omitted.
If you call someone disingenuous, then yeah, you're being offensive. But if you call the idea disingenuous, then it's much less offensive. If you phrase it like, "isn't that a little disingenuous?" it's even less offensive yet (I think "isn't that a lie" would come off a fair bit more offensive). Using "disingenuous" and words like it, I've had a lot of success finding common ground or at least identifying the locus…
Ideas can't be disingenuous because they don't have intent to begin with. Therefore, if an internet comment calls an idea or an argument disingenuous, it's calling the idea-holder or argument-maker disingenuous. It may be a little more indirect, but it's still an attack. In my observation, that word has the opposite effect of 'finding common ground', so I'm surprised to hear you say that. If finding common ground is…
I don't think that's required. If I call an idea "disingenuous" (or "misleading" for that matter), it doesn't imply that the arguer intended to mislead, but only that the idea lends itself to misinterpretation ("it seems disingenuous to suggest that the protest was violent on the basis of the actions of one or two out of tens of thousands" That's my $0.02, anyway.