Stupidity: The whole premise of the plan is summarized by Helen in the sentence "They don't know Andi is dead, so why would they suspect anything?" However, "they" conspired in unison to financially ruin her sister, and "they" did not answer the mail, none of them. The possibility that "they" all could have gathered and silenced her by force is one of the most likely ones, and yet neither she or Blanc consider even for a moment that the literal crime conspirators could have conspired.
Stupidity: The whole thing about the Klear energy source is that it is solid hydrogen. Claire as the governor of Connecticut supposedly signed off an entire power plant based on it. Yet not only she is mighty surprised about the fact that it has potentially flammable issues (but she herself brings up the Hindenburg), but also the whole meaning of Miles' machination down to the presence of the Mona Lisa, is to impress world leaders and 'unveil the future' showing that his home is powered by it. That does not make sense; if the energy source is so experimental that a single house powered by it is gonna be such a breathtaking reveal, there can't be a whole power plant in a major US state already signed off on that technology, that somehow involves literally piping the gas through homes.
Stupidity: The Disruptors have been close friends for well over a decade, and one of the other guests is Duke's girlfriend who has been living with him for at the very least one year (she was at the previous meeting). Yet nobody seems to have the slightest suspicion or recollection about his pineapple allergy, so lethal that it kills him in a few seconds, even more amazing considering that the favourite drink of one of those drinking buddies of his (who is sitting on his lap in one of the flashbacks) is exactly what would kill him; the topic of contamination surely must have been touched upon. (01:00:00)
Suggested correction: The disruptors were never close friends. According to 1:19:50, they were Andi's "pack." Andi discovered their potential in 2010 because she was an entrepreneur. They were so unfaithful to Andi that they had no qualms perjuring themselves in the Brand v. Bron case. At 1:27:07, Whiskey describes the group's relationship as fake. She says the group's gatherings are "the worst." The only things each of the Disruptors ever cared for was Bron's "golden titties."
Is the correction just about the usage of the adjective "close" on my part? I mean, fair, but I don't see how that changes the absurdity of the fact that these people (the victim's girlfriend and his "pack", "friends", "group", etc.) who have been hanging out at the bar, shown drinking together and established knowing each other for years and years, somehow are oblivious to the violent allergy of this person - something Duke himself is not secretive about and that they know would kill him with just a drop. It's the typical unrealistic dumbing down/forgetfulness of whoever in a wuddunit is not the main character (hence a stupidity, never painted it as a plot hole).
I get it. You say it is stupid that a group of friends know each other so poorly. I'm saying they were never friends. They cared for their own benefits. Hence, they never sought to know each other, let alone care.
Stupidity: Of course, it's a movie with a heavy comedic tone and it's a rather cathartic scene, but still it's worth noting that Benoit Blanc had no way to know that making the whole HOUSE (full of glass shrapnel, too) explode wouldn't gravely injure or kill anyone. What a ruthless fellow.
Suggested correction: The scene at point 2:06:02 suggests the opposite. Blanc knew the house would explode violently, hoped everyone would get injured, and sat watching it while helping himself and Derol to a cigar. Bron was guilty of two counts of first-degree murder. The remainder were accessories to the crime, having already pledged to perjure themselves. Their sentence would be death if it were not for their destruction of evidence. So, all Blanc needed was a sense of justice, not ruthlessness.
Helen, the innocent sister of the original murder, is in the building too. I wouldn't want to say that he hoped *everyone* would get injured, just the bad guys but that's the point. It's simply a case of an absurd decision that puts to mortal risk everyone but has no negative consequences "because movie."