It's not an excuse. I think that, pragmatically, taking Anders makes no sense as he's a GW and would have story content there. I just think the idea that, as a player, there'd be actual character death related consequences for not taking Anders along is very far-fetched becaus Bioware never plays out the logic of the setting like that.
The party was always immune from the taint, except for this one bit one time in DA:O, and only for Carver/Bethany. If you leave them behind, no one gets sick. It's contrived.
I agree this part of DA2 was completely stupid and terrible storytelling. Everyone is covered in darkspawn blood, everyone was injured by darkspawn blades, and only Bethany/Carver gets sick?
Oh and what about all that blood Bethany/Carver were covered with during the opening sequence of DA2? Why didn't they get sick then?
For that matter how did either one of them die during a cutscene at the beginning of the game? Every single cutscene death is completely contrived and completely stupid, especially when you know that if they got attacked while you were able to control your characters, they wouldn't be dead. The only reason they died is because every character, including them, stood around acting like an idiot with their mouths hanging open and drool hanging pouring out while the monster had their way with them and everyone else just looked on like "DDDUUUUURRR hat go on foot".
Even though I didn't really mind Carver dying cause he was such a whiny little baby. It was all "WAH WAH I'm not the center of attention. Everyone likes Hawke more because she's a better fighter than me. WAH WAH"
Or to use an actual quote:
"Carver: I am not a joke.
Hawke: No you're a lazy brat with a chip on your shoulder."
Here's how the Deep Roads actually went:
MORTICIAN: Bring out your dead!
HAWKE: Here's one -- nine pence.
CARVER: I'm not dead!
MORTICIAN: Here -- he says he's not dead!
HAWKE: Yes, he is.
CARVER: I'm not!
MORTICIAN: He isn't.
HAWKE: Well, he will be soon, he's very ill.
CARVER: I'm getting better!
HAWKE: No, you're not -- you'll be stone dead in a moment.
MORTICIAN: Oh, I can't take him like that -- it's against regulations.
HAWKE: Well, can you hang around a couple of minutes? He won't be long.
MORTICIAN: Naaah, I got to go on to Robinson's -- they've lost nine today.
HAWKE: Well, when is your next round?
MORTICIAN: Thursday.
HAWKE: Look, isn't there something you can do?
CARVER: I think I'll go for a walk.
[stabs Carver and hands him over the Mortician]
HAWKE: Ah, thanks very much.