"I don't see why."

Maybe it's a bit too simple of an answer for this situation, but Alice honestly can't think of a different way to put it. This just is the answer.

She folds her arms across each other.

"You've seemed sensible to me so far." As sensible as a child can be, anyway, which means that there's some leeway that Alice wouldn't give as much to adults. "If you stabbed someone, surely you'd have a good reason for it."