But what if someone else thinks differently? Will letting other players play as Origin characters diminish your playing experience?
Of course it will, because the game and the story won't be written the same.
Every characters you'll met in the game already have the same story, the same goal, the same problems.
The only differences is their backgrounds, maybe (idk) the way they'll use and probably side quest.
It's not really the same point but in BG it's not that obvious. If you don't help your teammates or they dissagree with your actions, they'll leave.
That's another way you personnalize your team and create your role play (good, bad, help him or not, personalities and goals, interractions and/or romance.....).
Same.exemple than before... You can't play jaheira or minsc as main characters because they have their own will and their own stories.
That's another reason why the world is coherent.