While this comment will probably go un-noticed due to the fact that I don’t want to type for 7 minutes, I’d like to emphasise the words from my post, “The most dangerous shinobi”.
People from Konoha such as Naruto, Minato, Guy, Jiraiya and Hashirama are in no way dangerous. They’re strong yes, but not dangerous. Same goes for villains like Sasori, Konan and Kakuzu.
The correct answer would have to be someone both extremely skilled and frightening to be around. I mean “we’re going to die” frightening.
The only people I can think of are Madara Uchiha and Orochimaru, and maybe Itachi because of his genjutsu.
I’m not even going to go into any details as to why they are my choices, but imagine you’re just walking past Orochimaru and he decides to use you for 1 of his experiments or reanimations. He’s not even angry, it is just research, like science, and for that reason he seems to be more dangerous than Kakuzu.
Why Kakuzu though?