This is one of those cases where Barnabas gets someone into terrible trouble without meaning to, but it's a damned sad thing that Cassandra took out her fury on poor Sam. Dragging the innocent into his feud with Angelique, leaving Sam blind, is taking it beyond just the two of them.
That's why I've always found it so difficult to like Angelique; she doesn't seem to care who she hurts or how.
This time I've got to blame Barnabas more than Angelique. I mean, when you're dealing with Angelique, you know you're dealing with a powerful witch who has no qualms about destroying anyone in her way. Sam might not have known that, but Barnabas sure as heck did! Didn't it occur to Barnabas that Angelique would be able to find Sam Evans and discover who was doing the painting? More than anyone Barnabas should realize the extent of her powers!