It takes the laborer eight hours to create a product for the capitalist. The capitalist then offers that product back to the laborer for twelve labor/hours.
If that was true, the laborer would just "create a product" and sell it to another laborer for 12 labor/hours.
Maybe you've left out some important details?
What you've described makes "laborers" look like complete fools,
obviously in need of your control to save them from their own choices.
The truth is that a free market allows everyone to engage in voluntary exchange.
Whatever deal the laborer makes, he makes it freely because he feels that it is beneficial to himself.
But you don't want the laborer to be able to decide what is best for himself.
And that is what socialism is about:
taking away people's freedom, their power of choice,
and giving all that power to a few people.