I suspect the person who said that wasn't terribly clear on what assimilated actually means sociologically, and was going off of emotions rather than accuracy. Assimilation just sounds nasty and has some (rightly) negative connotations for many people. I think the filmmakers fell down on the job in including it though. It may well be the sentiment meant to be expressed was something along the lines of "The less visible we become the greater chance we run of becoming persecuted against." Which is at least an arguable point. "Assimilated" and "less visible" are analogous in some ways, but I also don't think it clicks as actually accurate in this context.

Using an inaccurate word doesn't make you an idiot, it does make you sound ill informed, and is distracting and I'd bet we've all been there. Actually including it in the film is the bigger problem and hints at sloppiness. So rather than talking about the film's intended message/s we end up nattering on about production choices.

I think perhaps the better word would
be mainstream. "Assimilated" sounds like
something right out of Star Trek.

I also believe the issue is a bit more complicated.  Also...a teaser trailer is just that...a 'tease' of information.  I'm sure if you see the movie, then you'll better understand the context of "the more assimilated, the more persecuted..." 

Other parts of this trailer actually back up the assimilation comment even if different words are used.  I think it's a little overblown to jump on one truncated statement in a trailer that contains 1/60th of the information presented in the actual film.