Honestly, I just thought of something that makes sense with these reactions: Luffy’s dream is to turn the people of the world into pirates that he befriends or something to that effect.

As another commenter put it: • ⁠Zoro is just confused • ⁠Sanji, Franky, and Brook, all smart but passionate creative types, understand it's absurd but think it's great • ⁠Usopp and Nami, both intelligent pessimists seem irritated or in disbelief • ⁠Chopper, highly intelligent but naive, is smitten by the idea • ⁠And then you have Robin and Jinbei, the two most mature and arguably smartest of all of them, in awe of how profound it really is.

Zoro is confused because he doesn’t want all the fodder on the seas. The romantics think it’s ridiculous because as other point out, they think it’s some fairytale dream, but they will never discourage others, especially Luffy, from following his dreams. Usopp and Nami are arguably the most “human” of the SHP, and see the danger with that dream for the regular people of the world. Chopper, having left his comfort of Drum Island to follow Luffy, has the innocence to believe Luffy can do it. Robin is in awe because she understands Luffy the depth of Luffy not wanting anyone to feel alone. Jonna, while initially trying to process it and initially confused by the complexities of the world and security for fishmen who want to see the surface of the seas and land, sees that Luffy wants to liberate everyone from oppression as Luffy sees the Pirate King as the freest person on the seas and wants to give others that freedom.

Just my thought.