In the 40s, people feared invasion by foreign forces- the germans et al. They expressed these fears through films, with alien fleets invading and what not. This eventually segued into films like "Invasion of the Body Snatchers" as the public fear became not extermination, but communist regimes. In the 90s films like "Independence Day" and "Terminator 2" explored our fears of nuclear war beyond our control or understanding. Today, though, the fear is of terrorists- we have a completely unfounded terror of Islam. Once someone reveals themselves to be Islamic, or a car reveals itself to be a Robot in Disguise, we immediately (be it thanks to the media, racism or just a need to have an enemy) assume they are terrorists or- you guessed it- decepticons. This theme defiantely showed itself for me in the scene in the new Trailer where sector seven attack Bumblebee. A similar cocept was explored by X-Men. This is why as long as the film has likable characters and awesome action, it is already very clever and importnat indeed.