Les Écorchés - S2-E7
Stupidity: The highly trained, elite security officer who tracks Angela down to the backups knows exactly what she is, how dangerous she is, and what she's capable of, but still drops his guard, flirts with her, lets her get up close and personal with him, and as a result gives her a clear window to grab his grenade to blow up herself, him, and all the backups.
Laura Ingalls Wilder (1) - S7-E1
Stupidity: Charles and Caroline are dancing at the church social. Charles makes a comment about Laura getting married. Caroline responds with "I'm just dying to call you Grandpa." Mary's son just died. Charles has already been a grandfather. That comment was beyond insensitive, and just plain stupid as written. She should've said, I can't wait to call you Grandpa again.
Stupidity: Being a U.S. government-owned Secret Service vehicle, West and Gordon's train, "The Wanderer" is woefully lacking in security, as everyone from uninvited strange women to villains are allowed to just walk through the door of West and Gordon's private train car.
Stupidity: The emigrants lack guns yet after several bandit raids the team does not take the guns and ammo from the bandits to protect themselves from future raids. It's not like they can swing by the local Cabelas and stock up on guns and ammo.
Zorro's Ride Into Terror - S1-E8
Stupidity: When Diego sees that the passage door is opened, he invites Sergeant Garcia to sleep in his bed. However, Diego never tries to close it, and during the rest of the scene, nobody (even Captain Monasterio) seems to see it open.
Stupidity: After Walks on Cloud releases Dr Mike, she runs off and hides in a wild thicket as the Dog Soldiers and One Eye look around the area for her. A pair of buckskin are then seen scoping the area, then walking off as Dr Mike leaves her hiding spot and gets 'surprised' by One Eye, who knocks her out. She should have known better and stayed put until sunrise, as Sully taught her when it came to the Cheyenne war parties.