I would argue that there is no such thing as absolute ("real") freedom, if you define it as "total absence of any interference in your life from other beings" - this is only possible on the desert island.
You argue that even if you are at risk of being killed or enslaved you are still free until it actually happens, but this is inconsistent with the idea that government restricts your freedoms - are you still free until the point they actually come and arrest you? Modern governments pass laws which are (essentially) promises to come and arrest you if you do certain things, but it wasn't always like that - under medieval (or fascist) governments they might come and arrest you if you offended them, or if it was to their political advantage. Were you still free right up to the point when they came and took you away? Surely the same applies on the island - if you know it would be to some-one's advantage to enslave you and have you work for free and there's nothing stopping them from doing so, are you free?
On the other hand if we're using dictionary definitions:
2. exemption from external control, interference, regulation, etc.
3. the power to determine action without restraint.
4. political or national independence.
I would argue that definition 3 is the most powerful and general description of freedom. Surely definitions 1, 2, 4 are all special examples of that one, and it indicates a fundamental truth - that freedom is inextricably linked to power.
Using this definition, there definitely is no such thing as absolute freedom - even on the island you are restrained by your muscles and bones, by hunger, by your need to find shelter, by your finite intelligence. Only a god is absolutely free, but things like resources, technology, organisation and (yes) government each help make us more free.
I am aware that this is a different definition from the one you prefer, but I think it is the more important one. What good does lack of interference do you on a desert island?
I also agree entirely that the only direct thing governments can do is to restrict freedoms. However, they certainly are not the only thing that can restrict your freedoms, and if they restrict the person who would otherwise restrict your freedoms (by murdering or thieving) can they not be said to have the net effect increasing your freedom?