I played BG2 but not BG, so my views are skewed, but it seems to me that one of the few bold and neat things in the BG series is the gap between the two games, the marked shift in tone, and the way in which information about what happened in that gap comes in somewhat slowly and only by inference.
There is a fanboy impulse, one that I've certainly felt, that blanks in narratives are holes that should be filled, rather than negative space that is a meaningful part of the composition and must be left unfilled for the whole thing to come together. Recently, that impulse has been getting stronger and creators have given in to it more and more, whether we're talking about Star Wars prequels or comic book origin stories or spin-off series or whatever. This kind of fill-the-page mentality is probably bad for art. As a consumer of art, and a would-be creator of it, I'm troubled by the mentality (even though, or maybe precisely because, I'm susceptible to it).
I understand that people can say, "If you don't like it, don't play it, it's not like this is Lucas destroying the unenhanced versions of Star Wars." That's true -- I'm not even a BG fan to begin with, so I have no personal stake in what happens to BG, anyway. But these moves have spillover effects; if the game succeeds, it encourages similar behavior. Some new players who want the "complete" BG experience will probably buy the game and have their experience worsened as a result. This may shape them into worse consumers. Those who want this kind of filler material will become more insistent by having gotten it; I doubt even a crappy version of it will convince people these things are a bad idea. (See, for example, the Final Fantasy 2 sequel that Square made, twenty years after I dreamed how wonderful it would be if they made one; crap that begets crap.)
Finally, while the pool of gamer dollars and gamer hours is flexible, it does have limits, and some of the time and money that players devote to this won't go to original games like, say, Xulima. For someone concerned about the Vogelization of games, that is sad.