I never understood why he was so alarmed about seeing Laura. Obviously she was there originally and the family continued to the present time. It made no sense for Barnabas to feel he had to interfere at all to protect the family.
He intentionally distracts himself from his purpose of being there by involving himself in things not connected to Quentin & David in the present. Its like he forgets for a while his mission.
For all it's flaws, the 1840 storyline was mostly free of Barnabas interfering with events as they happened.
Finally, are we supposed to believe that with all the lookalikes that Barnabas has encountered through 3 different centuries, he meets a woman with the same name as one who died more than 100 years before and he automatically assumes she's the same person?