Nuclear power plants were built 10 years after fission was discovered. Fusion was discovered at around the same time, still waiting. lol. In the meantime, a whole industry of pseudo-science has formed around the concept of fusion power. Fusion can only occur in a sun which has a huge gravitational force which supplies the necessary pressure to initiate fusion. On Earth, we do not have a huge gravitational force, thus, we must artificially create one. Thus, in order to create an artificial sun gravity you need to expend a lot of energy. Thus, the energy expended will equal the amount of energy extracted. Thus, it is not a feasible option. Note – The laws of thermodynamics wont allow you to gain any free energy.