Brightburn (2019) review

Two caring parents, Tori (Elizabeth Banks) and Kyle (David Denman), rescue a child (Jackson A. Dunn) from a rocket ship that crash landed in their back yard, raise it as a regular human being, but right before his 12th birthday, he becomes 'activated' and is intent on obliterating humanity.  Stories about evil kids are nothing new - Children of the Corn, Firestarter and Damien: The Omen II spring to mind - but this has nowhere to go with its flimsy premise: one by one, innocent people get dispatched (usually gruesomely) for no reason other than they're easy targets, and this includes the pre-teen intergalactic killer casually wiping out his own family.  What good is a movie in which the main villain can't actually be harmed - Tori notices that he can be hurt with metal from his own ship, but she's not strong enough to take him out (Kyle tries to kill him with a rifle, but bullets are ineffective) - and the film closes with him on a rampage?  Is this really a warning about adopting?  Or some antinatalist decree?  Or did the writers not think it through, worrying only about how gory they can make it?