That changed because time passed and the public became more aware. The change will probably never happen with the chimps because even if they are taught to communicate, they still lack the ability to speak. Killing chimps will never constitute murder. Although there are many similarities between humans and primates, the differences stand out The intelligence of chimps has been proven, but humans have to come to some realizations before situations change. Humans certainly realize the similarities, but deny that the simians are close enough to deserve fair treatment.
Murder is murder.
There is no line to be drawn. Murdering a human is no different than murdering an animal.