Ah, yes, I understand your confusion now. You mean that you prefer free market capitalism to a planned socialist economy. When Trotsky says that labour will be subordinated to the plan, he means that the plan is labour's, and that society will determine the allocation of its own resources as it sees fit.
You could argue that the plan is not labour's, and therefore the working class is enslaved, rather than being self-determining (though I think you would be wrong), but you cannot, I think, argue that Trotsky means that Socialism is a concentration camp since concentration camps are not usually run by their inmates.