Technically, this slavery is self-imposed. If people can live without using fiat currency, then there will be no slavery. But it seems they'd rather have a unit of value and become the slave instead. In fact the slavery also comes from the fact that they are desperately dependent on the banks, so when banks failed, all their deposits will be gone, so banks must be bailed out
In a planned economy system like Soviet Union, the resources are allocated to each person equally without the need for money, thus this kind of slavery is not possible. But you have other kind of slavery from the communist governors, and you really don't know how much of your work went to the government, since most of your income are not salary but equally allocated food/residence/cloth. However, under such a system there is no motivation to improve, you get equally allocated resources no matter how hard you work
Is it possible to have a type of money without being enslaved?
To avoid slavery, this money must be created by a cost close to its face value, but then you have to keep the cost at a constant level to use this money as a universal standard of value. Since the productivity is always increasing, the cost tends to go down over time, to compensate for that, the supply should also shrink over time. From this point of view, the bitcoin design is on the right track
Enslavement is the right word. The first line of the Internationale says, stand up, you who don't want to be enslaved. (The lyrics have a footnote that the Party is an exception.)
Money is necessary in any society beyond bartering (which would be horrible.) As soon as you have money, you're introducing something which may not have intrinsic value, but represents real value in the world. As long as everyone agrees on the standard, there should be no problem, and there hasn't been for millennia.
The value of each unit of money, until states and banks learned how to manipulate it, always fluctuated with market forces, and humanity lived fine. In fact, the economy thrived under this system during the Italian Renaissance and under the Scottish "free banking" system in the 18th and early 19th centuries. (Scottish per-capita GNP went from half to equal of England's during this time.)
Bank failures would not be horrible at all, systemically speaking, if every "depositor" was fully aware of what they were getting into. The real trouble is the implicit (if partial) government guarantee that gave "depositors" a false sense of security to begin with.
It's a fiction of modern elite-inspired economics that the value of money must be managed or all hell will break loose. The truth is the opposite.