First, the unveiling of "good" Barnabas in the first place, not as a gradual transition caused by certain life events in the 20th century, but instead by zooming us suddenly back, without warning, to 1795, where we get to see, totally unexpectedly (to viewers at the time anyway) an utterly unstained Barnabas, who then is put through an horrific series of events that really make us ache over the innocence that's ripped out of him, when the bad rubber bat finally gets him.
I think throughout Barnabas' life, he was very self-centered and self-serving, vampirism not withstanding.
The current S Wars movies could be seen as a similar slide into inevitable doom... which can be very well done, but not in this case, so far.  I'd rather see any randomly chosen DS episode from back then, than either of the more recent SW movies.
Basically, Barnabas had poor judgment and was insensitive to the feelings of others.