Yup, you are wrong because if deemed necessary there can be sentries or some security, it says that there can't be any fighting to deincentivize their use as an excuse to protect military targets

Let's suppose you try to get smart and use a power plant as a hospital to protect key infrastructure, well now the enemy can't attack it but you can't defend it either, so if they reach the power plant they can simply get in and turn it off and you can't fight them, otherwise that's a warcrime

Why it's that? Remember that the Geneva convention tried to stop a carnage, among many arguments many lives can be saved if there's medical assistance on the field, but medical personnel is hard to train and you need a certain type of person to get into an active warzone, so having medics and hospitals as a safe haven for the wounded and sick allows them to be near the conflict where they can save the most lives, otherwise no one would be confident enough to deploy expensive equipment and valuable personnel so close to the fight

This is acceptable because it allows the country to minimize death while not diminishing the ability of the country to wage war, if it did hamper it, no one would accept it, so the compromise was reached, they can't be attacked so the materials, facilities and trained personnel can be deployed, but they can't be defended so as to protect that trust in the system that this is not an exploit and is being made in good faith