All states are instruments by which one class asserts its power over the others, this is true. However, if you stop your analysis there, you confuse capitalist states where the capitalists dominate the state with socialist states where the working classes are in charge of the state. Equating the two based on the presense of the state alone, and ignoring its class character, is a massive error. Where capitalism brings ruin and misery to the working classes, socialism brings liberation.