I already know what a few are typing. No getting beaten only to look good 3 chapters later doesn't matter. Luffy is a clown. Him getting punched and kicked like a dog doesn't have a lasting effect like it does  on a character like Shanks, Mihawk, Imu. On these type of characters it will remain a blemish. 

No Luffy is never wrong. Whatever action he takes is treated as if it's the best possible move.

His suicidal brain dead behaviour is encouraged by the author. Just look at Oda having the trash be his mouthpiece to basically admonish the reader. 

What would happen if his obscene plot armour got turned off ?

Luffy would have caused the deaths of his crew. He would have been dead more than a dozen times already. 

It's like gambling with your life and your family's life only to shit talk someone telling you to stop because for some fucking reason you keep hitting the jackpot again and again.  

He never faces consequences. Never feels guilt for his recklessness because his fuck ups never have a price. 

Oda has contradictory actions and phrases. 

He treats the MC as a hero but has characters say shit like we are pirates. Then they have double standards both in story and One Piece fans outside of it. Should Luffy ever do something morally dubious then he is a pirate. Totally disregarding how the story treats him.  

Has them be heroes and hate evil people but team up with violent mass murderers when it suits them and Oda closes his eyes and never brings the matter of the other guy being evil because they help Luffy now. Remember Nico Robin ? 

She should by all means have been punched off the ship but the plot warps into them accepting her and Vivi never doubts or dislikes Luffy's actions.

 Everyone always accepts Luffy's actions. That's not how people work. 

You have Usopp and Luffy talk about how running away is fine and then you have them talk about fighting to death a few chapters later.

Oda treats his MC too well. A good parent must make sure there is a balance between vegies, meat and dessert. Homework and playtime Oda gives Luffy only dessert. He refuses to have Luffy be wrong. Refuses to have Luffy lose  a fight. Luffy must always say the last word.