Why so many negative reviews?

Rating: 8/10 (22 November 2012)

I watched this one in a dollar movie theater. And I didn't plan to watch any particular movie. I did take a look of IMDb before watching it. The only thing I was aware of was that the user rating is quite good (7.9). But I have no idea what the movie is about before watching it.
Overall, I did enjoy the movie. One can say the plot is predictable. But really? Almost all Hollywood action movies are predictable if one puts it that way. At least I would say there are several possibilities that the movie can end. Of course, the current ending is one of them. But to say it is really predictable is kind of unfair, at least one cannot be sure if it should end this way.
Now. The thing really puzzles me is why the movie gets so many negative reviews. Even more puzzling is that the movie itself actually gets pretty high user rating. One conjecture I made is that many reviewers feel that they are physics experts and to them the time machine part is not "logical". A common complain is how the whole thing would have happened if Joe killed himself at the end. I am not sure those "experts" heard of parallel universes (http://en.wikipedia.org/wiki/Many- worlds_interpretation) and if they really care about accuracy interpretation regarding science, I'm not sure why they don't complain about the time machine in the first place.
I believe another source of negative reviews originates from the controversial part of kids getting killed. But come on, this movie is rated R. And I don't agree to some reviewers that the kids were killed for no reason. The motive of old Joe is totally reasonable and he did show remorse for his crimes.
In summary, I would argue that most negative reviews are biased not based on how entertaining the movie is but on how "correct" it is regarding "science" and "morality". If you care a lot about "science" and "morality" in a movie, please avoid this one at all cost. If you just want to watch an entertaining action movie that doesn't have many logical holes (definitely not more than the "superhero" movies), by all means please.