Why was Watson so unfair to Rosalind?
a) Watson attacks Rosalind's personality because he can't really attack her intelligence or her work.
b) He shows himself to be vengeful towards her after she inspected and thoughtfully dismissed their early attempt at building the DNA model.
c) As he makes Rosalind out to be difficult and impossible to work with he may be justifying that he was involved in the injustice of taking advantage of the clues Photo 51 held—even though she didn't knowingly share the Photo herself.
d) Well, if he threw Rosalind under the bus (so to speak) it would attempt to sway the readers about Rosalind and her character.