Our physical brains? As in the very brains that we are trying to work out if they are purely material or if they are a simulation? If your argument assumes that they are purely physical to start with that's called begging the question.
You cant say "we know purely material brains give rise to consciousness because our brains are purely material and they give rise to consciousness" within the context of a discussion about whether our brains are purely material or part of a simulation. Because if we "knew" that, then we'd already know the answer to the very thing we are calling into question. And if we already "know" that our brains are not a simulation then there's no point having a discussion.