I've said it before, and I'll said it again: Ben's not very bright. One minute he's wondering how he can warn Barnabas, the next minute he's trying to figure out for Angelique how she can keep Jeremiah from leaving, and a couple of minutes after that he's laughing in delight because she's turned Joshua into a cat.
One of the things that gets to me about the 1795 storyline is that it's the good-heartedness of people that brings them down. If Angelique's original plan had worked out - if Jeremiah had gone to Barnabas when Josette first came on to him, and if Barnabas had played the outraged lover and if Josette had been sent home to Martinique in disgrace - well, then, Josette would not have taken the dive off of Widows Hill, various people would not have died in various fashions, and Barnabas would not have become a vampire. But Jeremiah gave Josette a second chance. So Angelique made Jeremiah fall in love with Josette. Jeremiah resisted. And so on. At every stage of the game, the Collinses and the Dupres tried to keep things on track. And Angelique never looked at them and said, "These are good people. Maybe I should leave them alone." She kept going on, and on, and on, and so the well-intentioned actions of various people kept getting them further into the soup. 1795 is a grim business.