luffy went to onigashima to fight with the natives of the country.
perhaps his original reason was to find the burned mark man in elbaf, but he clearly  wanted a fight the moment he found out they were red hair's men.
here is what killer says before this scene happens ,
	
	
		
		
	
	
	
	
		
		
	
	
this conflict didnt need to escalate in the way it did
kidd's actions did that.