Thats Luffy's character, he is selfish and reckless but he would still die to protect his nakama. Luffy likes to leave things for chance, he willingly choses difficult and more adventurous path which in turn helps his crew to become stronger. Not to forget all of them accepted to sail with Luffy on Luffy's terms, he is the captain after all.
like i said the new world is what brought the worst aspects of it.
and apparently the crew members only joined luffy because he has quality to make everyone wants to help him
what mihawk said destroyed the value of everything that happened before marineford.