It is a hidden transaction. They try to argue it both ways, that it's an exchange of access for data, but then they hide the data in the fine print. When you buy something, the price isn't in the fine print, it's front and centre. When you buy insurance, they have to provide a "key facts page" where they detail what you're paying for in general terms. The key parts being exchanged are supposed to be at the forefront, not hidden in the terms and conditions.
People don't understand the value of their product because businesses hide that part in the terms and conditions to inhibit their ability to properly assess the value.
In your analogy, you asked them to send your nuts and bolts for free. In exchange, they advertised stuff to you. Then they started collecting the addresses of your clients... that was not fine. Now, they're throwing nuts and bolts from multiple people into a box and selling it as a "sampler kit", nuts and bolts you did ask them to send for free.
I didn't ask them, they advertised their service in bright lights saying it was free. Then, the fine print at the point of entry says they can pick the pockets of their guests.
You really are trying to advocate for the devil here, and I think if you take a step back you'll see that you're just parroting the same arguments they make. Such arguments have not been properly challenged yet, but if you stack them up against the core principles of contract law - through which all trade is conducted - they are clearly wrong.