Well, it is true that movies this summer (as a whole) aren't doing as well as expected. And you do bring up a good point that it may have just been a lack of interest in the film itself... Cruise's public image might just be an easy scapegoat for analysts. However, given is previous success with action films, you can certainly make a good argument that since his popularity has dropped off massively, it hurts this film's chances at the box office.
And yes, it is true that no one forced him to make all of those public comments. But there are plenty of other stars out there who have said and done equally outlandish things. Unfortunately for Cruise, since he was (arguably) the biggest movie star in the world at the time, the media turned him into a pariah.