The only objective you would have in mind while preparing a poster is that it should catch the maximum attention of the public and create that curiosity. This is a much needed thought indeed and the creative team works exhaustively on coming up with the right poster.
However, it is also important that the makers need to realize where they must draw the line because it is also about public reactions. While this is morally right, controlling such things is tough in internet. The latest is about the poster of the movie Danger.
The poster shows a severed head in a plate and it is rather gruesome. As such, these types of posters are created with the sole purpose of gaining a lot of attention and creating that hype. Many are now demanding that the poster of the movie Danger must be banned.