We’re just lucky he still had enough of an edge to lie to Negan about Maggie.
If not for Carl’s stand against the Savior, Negan might not have confiscated all the firearms at Alexandria.
Sure, the lie will probably backfire spectacularly once Negan discovers that Maggie is alive at Hilltop, but at least she’s presumably recuperating among allies for now.
If Carl had been ready, he might have been able to hold his temper and stop himself from pulling a gun on a Savior.