They can take it off, but in the books it was noted that John, Sparten-117, felt aucward (please don't flame for spelling) walking without his armor. This is because the armor reads his neural inpulces and moves with him (like using a second pair of arms and legs over the original). But then again, the only time we ever saw a Sparten in the Halo series NOT either getting ready or already in battle was the award ceramony at the beginning of Halo 2. Because of this I can see where one can get confused, I hope this information has helped you.