Banno the belief is not justified, nor is there a choice involved. I don't make some kind of justification for these kinds of beliefs, that's Wittgenstein's point. Moore justifies "here is a hand" through a proof, an argument (look at my last posts in
A Wittgenstein Commentary where I quote Moore), but Wittgenstein refutes this idea. There would be a justification involved if you asked me how I know that there are pens, paper, clothing, etc. in the room, and I replied with, "I saw them." Note that now this is taking place within language, which is where justification takes place. Justification is linguistic.
Think about it this way: You walk in the room and see the objects, as a result of seeing the objects you have the belief, there is no choice, and there is no justification needed. Do you justify the belief to yourself? No. The only time a justification would be needed is if a discourse takes place between you and someone else, i.e., you are asked, "How do you know...?" Also note that this e.g. is different (in terms of justification) from Moore's e.g., in that everyone sees Moore's hand, Moore holds up his hand to the audience and says, "Here is a hand." "Here is a hand" is bedrock, there is no need to justify this belief to the audience. Wittgenstein's point is that these statements are bedrock, they are the hinge on which justification occurs. The epistemological door wouldn't swing without these beliefs.
There is also something that is
the same in my e.g. and Moore's example. Everyone in the room with Moore is having the same sensory experience that you have when you walk into the room (my e.g.) and see the objects I mentioned in my e.g. Where Moore goes wrong is that he is using a justification where no justification is needed, just as in my room e.g. Do all the people in the room need a justification that that is a hand? No. Do you need a justification when walking into a room that has x, y, and z objects? No.
You need a justification where a doubt might arise. So if I'm not in the room, where either e.g. is taking place, I might ask, "How do you know?" This is perfectly legitimate, and it's within your epistemic rights to ask "How do you know?" Then, of course you can give your justification, "I saw..." The justification is a sensory justification, which is one of the ways we justify some of our beliefs. Thus it would be a piece of knowledge.
There is a further point however that seems to be confusing, viz., that there are two kinds of bedrock beliefs. First, there are those that take place within language, as in Moore's statements. Second, there are bedrock beliefs, which I'm identifying, and which Wittgenstein alludes to in
On Certainty, that occur quite apart from language. These bedrock beliefs are the ones I've given when talking about pre-linguistic man, but also note that they do occur in my e.g. above, viz., if Banno walks into a room and sees x,y, and z objects, then you have these beliefs; and although Banno can state the belief (something pre-linguistic man cannot do), they are not stated until they are stated. They are not stated in your mind, you have them quite apart from any statement, a statement is not required in order to have these beliefs. If you want to share the belief, or justify the belief, you can, but that's not a necessary ingredient to
having the belief. This is why pre-linguistic man can also have the belief quite apart from language. He could walk into the room and see the same objects you see, and as a result have the same beliefs you have. The only difference is that he cannot share the belief, he doesn't have the linguistic ability, the same is true of an animal.