You have a nice life. Someone comes up to you and holds a gun to your head. You are now about to die. They say "I won't shoot you if you give me all your money".
Suddenly, giving away all your money is in your best interest. Therefore it's voluntary, and by your argument, fair and reasonable and nobody is being taken advantage of because it's all by choice and in best interests. Right?
That is incorrect. By holding a gun, that person has initiated force against you. Initiation of force is a proactive action that requires volition on part of the perpetrator.
Amazon is not initiating force against anyone. If they provide higher than market wages for the workers, they will be violating the rights of their shareholders who will lose money and will be worse off due to the deal. In an industry with as tight margins as Amazon, it can result in flight of capital, loss of shareholder value and layoffs.
comments I haven't verified state that the people had a welfare state income keeping them alive, and that by merely extending an offer of work - at any salary - Amazon causes that to be revoked.
This isn't literally "initiating force" but if it is true then it is very similar in effect to the mugging scenario, and having the mugger use unseen but still present power to "make an offer you can't refuse" is still not a fair and ethical way to egg people to voluntarily enter into contracts.
You have a nice life. Someone comes up to you and holds a gun to your head. You are now about to die. They say "I won't shoot you if you give me all your money".
Suddenly, giving away all your money is in your best interest. Therefore it's voluntary, and by your argument, fair and reasonable and nobody is being taken advantage of because it's all by choice and in best interests. Right?