The audio isn't just the script. If it was, a text-to-voice system would be sufficient. Inflection, timing, etc. How and when something is said can be pretty important and these things can add a lot to the artistry and execution. These things are often lost or at least changed in the localization process. The point is that I want to experience how it was meant to sound. I want the experience to be as close to the original as possible.
Also, a lot of fansubs (not all) tend to be light on localization, heavy on literal translation (with notes explaining context when deemed necessary). I prefer that approach for basically the same reasons, especially since over time, you tend to learn more and more of the context and so localization becomes unnecessary and undesirable.
I guess it's simply different strokes, then.
I'm very much a fan of the writing process and the execution, which is why I enjoy subs and dubs equally. I'm no particular stranger to either of the two, though it'd be impossible for me to say I've watched as many subs as I have dubs.
There are various cons to each. With subs there's having to look down to see the subs (not always a problem, especially if you're watching on a computer or the subbers are courteous enough not to drop paragraph bombs on you) and subbers can get super liberal when trying to match the words to the mood (My favorite examples include "Tits McGee" and "What the shit", the latter translating "Nandayo"). With dubs there's a smaller pool of voice actors and Bryce Papenbrook exists. They each have their problems, but for me it's also in their specific charms that I can gravitate towards one or the other.
For instance, I couldn't watch Steins;Gate in English because Okabe's laugh and his overall voice don't match his personality as much, Mayuuri can't "Tuturu", and Makise's a cynical asshole. But on the flipside, they managed to make a joke where Okabe speaks English to a guy equally as funny in English- though in the case of the former it's because of Okabe and in the latter it's because of the response.
Then there're shows like Cowboy Bebop where the Westernisms get me in English, Yu Yu Hakusho where the dub does a much better job of portraying the main character than the sub/original does (Excel Saga's first Excel does this, too), and B Gata H Kei, where the euphemisms are colorfully delightful.
But in gaming and anime, I've always been huge on examining the various parts (art, animation, writing, music, etc) of how a production is made, so I can certainly respect where you're coming from and, hell, I don't completely disagree with you. I'm not a purist by any sense but I'd be lying if I wasn't interested in the same thing. It's just that I'm big on the adaptation process so it's just something else for me to enjoy in dubs (though, again, I hold them in the same regard as subs, albeit for various different reasons). Then there are older dubs like Those Who Hunt Elves which is so liberal (though less liberal than, say, Pokemon or Samurai Pizza Cats) that it's far more enjoyable than the original. It's the variety of the various dubs, subs, voices, and overall writing choices that I just love about Japanese games and anime. It's fun.
Similarly, I don't particularly have anything against those who don't like subs- I can understand the reasons for such and, generally I don't mind, but these ideas that all dubs are bad or that they betray the original meaning of the work, those bother me because the former...well, if you think that I'd imagine you just had a bad first impression, since the idea that all dubs (or even most) are bad is pretty obtuse. In the case of the latter, well, I've already spoken on that twice on this page, and I honestly don't get where the notion comes from except for, possibly, older anime where dubbers could get as literal as they liked. Altogether, though, these notions just seem dated and inaccurate. Like what you like, but don't rag on something you haven't actually experienced.