Why did Lorca suddenly care about other creatures (ones hes never met, and actually betrayed him) and want to defend them from Klingons despite even not knowing if the Klingons would attack the planet? Its insulting to the viewer to just randomly disregard a character's pre-established traits and act in a way that totally contradicts that without any explanation as to why.
Other than the fact that Saru would have kicked up a gigantic stink? For an excuse to attack the Ship of the Dead. He knew it was coming and was itching to provoke a confrontation, so he could order his crew to figure out a way. Remember he knows Admiral Cornwell wants him gone, and he doesn't know whether she'd given that order or submitted her report before her capture. A confrontation before the next visit to a Starbase was his only certain option to fight the Ship of the Dead.
I beleive again you're falling into the same trap - that is, ignoring Lorca's pre-established traits. He doesn't give a shit what Saru thinks. He has ignor