Only time i am sypathetic to the replicants
is when Roy dies and lets go of the dove , most of the time they just seem dangerous and viscious , apart from Rachel
I know this is an old thread, but Roy and his fellow Replicants are "dangerous and vicious" because they basically carried out the equivalent of a slave revolt to get to earth, and any human they come into contact with is likely to either kill them or report their existence to those who want them dead.
The genetic engineers they kill are pretty much equivalent to slave breeders. Sebastian for example is partly responsible for the Replicants having a four-year lifespan (hence his remark "there's some of me in you" after it's noted he has "Methuselah syndrome.") It makes sense why a Replicant would hold them in deep contempt and kill them.