This is putting Barnabas's pathology mildly . . He was always stubborn and dumb on many fronts. . He never saw what was right in front of him. He could've left Collinsport with all his money, a groveling servant and a ready and willing female at his beck-n-call. Its more than selfish that he stays on at Collinsport when Angelique's crusade against "him" is what puts the present-day Collinses in jeopardy. . . . .was this a 18th century ignorantly chivalrous trait or lazy writing?? ?!?
The more imperfect the person, the more material writers have to work with. Those who usually do the right things or the smart things can be admired by the viewer but they won't get much screen time. What kind of storyline did the character of Vicki ever really have after her introduction? She was nice. She believed in the best of people for the most part. She was dull. The decision to make Barnabas go back and forth combatting his demons (and stupidity at times) made for a ton of possibilities for plots and interaction with other characters.
If Barnabas did the smart thing and leave as you suggested, that is one less complex character for the series and less story material.
Look at how horror movies work for example: someone ventures into an area (or a house) after repeated warnings or knowing people have been killed there before, etc. The Blair Witch Project: how dumb is it to go into woods that are unknown to you for what you know will be one overnight stay at least and you don't have any kind of walkie-talkie, cellphone or backup in case something goes wrong? Someone falls and gets a deep cut, or breaks a leg? People on that kind of a mission make contigency plans. Why dumb down the three students before this trip into the woods? If they had any of that prepared ahead of time, they would not have been hopelessly lost and things would not have progressed as they did. Hence, no movie. :-/