You're talking about getting onto an enclosed, protected space. You have the Constitutional right as an American to not be unreasonably searched, but that doesn

You're talking about getting onto an enclosed, protected space. You have the Constitutional right as an American to not be unreasonably searched, but that doesn't mean you have the right of free movement to any and all places not owned by you personally without restrictions imposed by whoever controls that space, even when it's the government. If you're trying to get into a courthouse, the white house, an airplane, a train, they can search you first. What happens if you refuse a search is you leave the platform and get back onto the street where you're allowed to move about freely without being subject to search.