Ntm the man only cares about his friends. If Luffy was given that decision he would do it with no hesitation. As for if Shanks could actually get hurt by that I just think there was no time to react and he was really thinking about it strategically.
For me that was just a plot filler . There is no way a sea king would have done that to Shanks We saw that Rayleigh swam thru the Calm Belt which is infested with sea kings and didn't have a scratch on him. Soo for me it was just a plot fill nothing else.