There are a few personality quirks I can accept as constants when it comes to Luffy:
Simple-mindedness: Falling for mind tricks and being easily manipulated (ie Jango's hypnosis and Miss Goldenweek's color traps). Also his tendency to forgive and forget easily. Luffy just isn't Luffy without that.
Determination: I admire his resolve when facing his enemies. It's always fun to see the hero overcome odds to achieve a hard fought victory.
Stubbornness: His wanting to head to an island whether it presents danger or not. And not hearing a sensible word from his crew against it. Because face it, when Luffy sets his mind on something, he will not let it go. And besides we probably wouldn't have as much fun as readers if he didn't go adventuring to those dangerous places. However…
It's also one of his worst qualities. When it comes to fighting, Luffy has a tendency to push himself near death and he gives his crew endless grief because of that. One moment that stands out is the end of Thriller Bark. As Luffy lay unconscious, Zoro negotiates with Kuma and offers to shoulder Luffy's pain. Being the tank that Luffy is, the kind of physical pain he experiences is beyond the average human. And while Zoro is no average human himself, it is undeniable that the burden was too much for him. It's worst because Zoro's pride prevents him from telling Luffy and it upsets me that Luffy doesn't bother to look deeper into Zoro's condition (maybe that might be asking too much, since when has Luffy been introspective? lol). His reaction was just, "I feel great!", then he moves on, despite seeing how unusually more damaged Zoro looks compared to the other strawhats.
I dearly wish Oda will use this as a future plot point. I want Luffy to know about this and be absolutely guilt-ridden. I'm not saying this to be a sadist, but so far, Luffy is only concerned with growing stronger. Given that this is a shonen manga, having dialogue that boils down to STRONGER THIS, STRONGER THAT, and that strength usually only means physical growth, I can to some extent, accept that progression. But how about along with physical growth, he shows EMOTIONAL growth? Luffy hasn't shown much emotional maturation since the time-skip. There was that time on Saboady when he ignored the fake strawhats taunts and went on with his business. That was okay. And he hasn't yet pushed himself to the point of death. Although that remains to be seen, since he's facing Doflamingo in upcoming chapters.
tl;dr - I want Luffy to learn that he makes mistakes that could cost him his life or his crews' lives and learn from it. It bothers me that he babbles on about wanting to grow stronger and better protect his nakama, but his recklessness indicates the opposite of that. He should be more considerate of his nakamas' thoughts and counsel.
Very interesting post and arguments. However, I kindly disagree that Luffy's only concern is physical strength related. Luffy has shown on multiple occasions that he is an outstanding human being when it comes to mental growth, sympathy for others and putting the needs of his crew above his own. Hopefully, some pictures will help my case:
! !(http://www.onepiecebay.net/manga/mangas/One Piece/081 - Tears/One_Piece_v09_198.png)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/099 - Luffy Died/One_Piece_v11_177.png)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/099 - Luffy Died/One_Piece_v11_182.png)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/152 - Full Moon/17.jpg)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/166 - Luffy VS Vivi/18.jpg)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/224 - Never Dream/One Piece - 224 - 19.jpg)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/388 - Gear Second/One_Piece-v40-221[Null].png)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/398 - Declaration of War/One_Piece-v41-202.png)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/520 - Gorgon's Eyes/One_Piece-v53-167.png)
! !(http://www.onepiecebay.net/manga/mangas/One Piece/521 - The Hoof of Celestial Dragons/One_Piece-v53-172.png)
I Think the pages clearly depicts a man who is not only emotionally mature but also a genius in the ways he expresses these emotions. Naturally, as Luffy had a rough childhood and was raised with bandits, one shouldn't expect him to express his emotions in a soft way, that doesn't mean the lack of said emotions, as I would argue that Luffy is one of the most caring and humane people in the One Piece world, although in his own beautiful way. His emotions regarding others are shown subtly and not forced on the reader, you see they are the kind of emotions he had after defeating Usopp, after burning Going Merry, his acknowledgment of his crew's strength multiple times and especially after the time skip as he trusts them enough to hold their own against New World opponents. Zoro, in particular, shares a great bond with Luffy as they both understand their similar role of being the strongest members of their crew, as well as the responsibility they have to upheld the safety and integrity of their group. Sanji as well understands this and comes next in line of shouldering the responsibility of the Strawhats. How many a times has Luffy stopped worrying about the crew when he knew that either Zoro or Sanji is there with them? A recent example is his entrusting the crew to Sanji even against the troops of a Yonko. Zoro's and sanji's quarrel before Kuma as well as Zoro's Ultimate sacrifice are great examples of how much a crew can go for their captain, as Kuma acknowledged this while taking his leave. A crew won't go so far for someone who is only obsessed with strength, in my humble opinion.
Regarding Luffy feeling guilt, Ace inspired Luffy in many ways, one of them would be the desire and ability to live guilt free. And while a broken Luffy lost his composure after Marineford, with help, he is back on track to being his real self. Also, Luffy is in a way similar to Blackbeard and his fatalist tendencies, as Luffy will do all he can for the people he cares for, he will do all he can to experience a great adventure without worrying too much about the consequences. The contrast between him and Teach lies in the difference of their views regarding nakama and how to achieve their respective goals.
In short, Luffy won't suddenly and hastily change and decides to go comfort Zoro after each wound that is inflected upon the green haired unofficial first mate. Some men converse in subtler wordless methods, for some words and emotions are better relayed silently.
Thank you so much for reading my words.