That he needs to stop carelessly putting everyone he cares about at risk because he wants a good fight.
It's been happening since Piccolo, and I'm not sure if he will learn in this arc after they added that halfassed bit about him actually saving a universe in order to shift blame away from him.
Not sure how it was half-ass since it's within Zen'o's character and the manga laid it on even thicker. Goku's selfishness having overall good results also isn't anything new, Vegeta for example.
And even if Goku does kill everyone because he's fight happy, he isn't going to change. The sooner fans accept that, the happier they will be.