Well it's technically free but it's not enough to have in your house, is it. And no-one wants to go to public toilets all the time [or maybe they do]?
Think of it this way. Basically tampons will be similar to condoms. If someone needs some they'll be able to get some for free somewhere. Equally, if someone wants to buy some they can do so. Should toilet paper be the same? Maybe. But tampons aren't setting a precedent.