Yet despite my very opinionated stance on this and many other things, I actually am rather laissez-faire when it comes to defending my favorite games, shows, films, etc. Sure, I might argue that Pootie Tang is a movie far more clever than even Chris Rock would admit and I will try to defend it, but someone calling the movie terrible doesn't irk me nearly as much as someone bashing an North America adaptation of a Japanese product.
At times, I wonder why I can brush off an attack on a fictional work, but then get upset over the same words directed toward an adaptation. But the same answer always stares me in the face; because while attacking the product can affect one's view of the work, attacking the adaptation destroys the adaptation as a viable work.
Normally, if someone rips on something they don't like, they usually exaggerate part of an episode, or a season to comic propotions. While this is a distortion, this can easily be countered by looking at the actual product itself. While many people will be dissuaded from doing so in the first place, the product will not be changed by the opinions shared by other people. It may be ignored, of course, but it will still exist.
However, people who tend to prefer subs don't just make fun of the dub. They actually do out of their way to "inform" the ignorant, in the process spoiling the series. Also, since dubs tend to come after the original show has begun to air, if the series is a long running-series, then future works of that same series will be dubbed in a manner more consistent with the original version due to the outcry that has been stirred up, and if retcons don't ensure that the "erroneous" dub was a mistake, a redub will essentially erase the flawed product out of existence.