@Jabra:
How much time do you think passed from the moment Franky obliterated B&B5 and the other Straw Hats arriving at the scene? Because you make it sound like he stood there for several minutes twiddling his thumbs. Yet everything happened back to back, he couldn't even quit because he was already interrupted by the others. Everything happend within 3 pages:
1. Defeat of Baby5 and Buffalo, Franky spots Caesar on the last panel
! http://img.mangastream.com/m/51/81646462/9ccd3e1918464f1c12a0e02c4749cd74.png
2. Franky is surprised that they can still stand up after taking a Gaon Cannon and realizes that they are after Caesar. Note that the last panel already shows the Straw Hats almost leaving the tunnel
! http://img.mangastream.com/m/51/81646462/4de6043fec2ab338df3dc6e0275f9bc2.png
3. The final page, the Straw Hats burst into the scene and Franky is surprised/distracted/comments on the situation. The Straw Hats and Law fight over the leftovers that are Baby 5 & Buffalo.
! http://img.mangastream.com/m/51/81646462/8193022113cb5135f0cc18167122f2c2.png
So the question is
Where would you squeeze this moment in, especially when we consider that even Law wasn't "allowed" to take action?
I think you view manga time too realistically. It's a medium in which characters can have a conversation in the middle of an attack. Time is perfectly happy to suspend for such things. Franky doesn't have time to make a comment? Please.
What did Franky do after he confirmed that they were after Caesar? Nothing at all? His one comment completely ignored the enemies. So yes, he quit. Blame the author if you wish, I don't care. They could have stopped existing in his eyes at that point and nothing about the chapter would change in the least.
And Law may not have been "allowed" to take action, but he certainly had enough time to.
Do what to allies? Randomly attacking them? He was perfectly aware that his crewmates are inside the lab (hence the line "I was getting tired of waiting"). And now 2 unknown entities fly towards him, in the New World, on a more than just hostile island. I would have fired too.
He was also perfectly aware that he was allied to another crew he wasn't really familiar with. Franky's not the first character to shoot first and ask questions later, and that's fine with me, but it's really hard for me to view that policy as anything but not very bright. Being dumb is fine too. We all know he's not the only one.
In the end I think I just have a different view of Franky in general. Oda builds many of his characters and their quirks on stereotypes, and in his case I just see traits of a "typical" daredevil with a manly interest in gadgets (and since this is One Piece, robots). When he entered Choppers body he wasn't worried or annoyed like Nami. He played with a new toy, an unusual gadget. "Fuck the manual, I'm a manly man who doesn't need instructions". Thats how I interpreted the scene. And the "pirate button" incident felt similar. "Manly men push buttons, I'm supa and I can't resist". Can it be considered dumb? Maybe, but I prefer to call it reckless. At least I'm convinced that he isn't dumb enough to think that Buffalo & Baby 5 where really after his cola, as hilarious that might be.
Why can't it be both? Pushing that button was dumb as hell, regardless of his thought process. Or maybe you could just say that his thought process was dumb as hell. He was even warned about what that button did ahead of time.
The traits you see of Franky aren't wrong or anything. And they could even help to explain Franky's stupidity. They don't nullify it, though. He's still doing dumb stuff.