Because that's the sort of thing all heroes (all of them) often do and we are expected to now think about.
Because stopping to ask Barbara and leave the kid with the cops or something wouldn't make for a story and is narratively boring and kills the pathos created by the meeting with the kid and the dossed mom.
Because Jason was emotionally very stressed.
Because he meant to be there to find a regular working place, not a drug factory, if I recall.
Because he entered the building thinking he would find the parent and exit with him alive and reuniting parent and son, who would be finally safe.