If you click over to msn movies, you can check out an interesting list of dumb movie moments that have taken place in the sci-fi genre.

The debatable list includes moments from The Empire Strikes Back, Signs, Alien, Terminator 2, Independence Day, The Fly, Jurassic Park, The Matrix, Superman: The Movie, and Contact.

Source: http://www.scifistream.com/2009/11/debate-on-the-dumbest-moments/