Because he is the captain, he always gives the best relationship for all crew.
To find such loyal companions... your son is indeed amazing... Dragon.
Recruited all the crew mates personally, Luffy cares tremendously for his crew. As far as captaincy to Luffy is concerned, he sees his other crew mates as equals in contrast to other pirate captains, who mostly sees theirs as subordinate underlings (his crew mostly calls him by name, rather than with an honorific or "Captain"). In fact, it could be argued that he is the only one that is generally beaten up and ordered around on the ship as several members of the crew have shown, especially Nami who never hesitates to give Luffy a beating for his idiocy (albeit, in comedic fashion). Luffy only pulls rank when he wants to go "adventuring", despite what his crew thinks, examples being when wanting to go to Skypiea and following the swaying needle to the New World.
Much like his idol, Shanks, Luffy is the kind of benevolent pirate captain who does not seek to actively harm others unless they give him and his crew (or anyone he cares about) a very good reason to. However, during the Jaya arc he was willing to start a fight with Blackbeard over a difference in opinion on pie. And as the Straw Hat Captain, Luffy has utmost faith in his crew.
