This is the tagline for the film Alien, which was directed by Ridley Scott, not James Cameron, as currently stated on this site. Cameron directed the sequel, Aliens.
"In space, no one can hear you scream." is on e of the most quoted and parodied timelines in film history. It would have been more accurate if applied to Cuaron's Gravity, in which the silence of space plays a role in the narrative.
Old hippie expression for accepting another persons statement/oppinion even if you do not agree with them, because you respect the other persons right to their own oppinion and freedom of expression and speech.