What are the drawbacks of nuclear fusion?

List of Cons of Nuclear Fusion
1. It is extremely difficult to achieve. 
In stars, strong gravitational forces and high temperatures naturally create a fusion environment. But here on Earth, we are facing the challenge to make nuclear fuel hot and confined enough to start a self-sustaining ignition.

Imagine trying to contain the plasma (a gaseous mixture of deuterium, tritium atoms and ions, and helium the fusion product) at 100 million degrees celsius. No material can withstand that temperature. So, scientists attempt to keep the plasma (being electrically charged and having a magnetic field of its own) suspended in a magnetic field produced by superconducting magnets around the fusion chamber/vessel. This is similar to how bullet trains float on their tracks at ridiculous speeds. This process is very difficult to achieve (as compared to nuclear FISSION).

2. It produces radioactive waste.
Though nuclear power plants only emit negligible amounts of carbon dioxide into the atmosphere, its nuclear fuel chain process does produce radioactive waste.

The radioactive waste produced with fusion is not the same as with fission, and the two are often confused. With a nuclear fission reactor, the radiation is alpha particles, beta particles, and gamma rays (which can penetrate your skin and break apart the bonds in your DNA structure, giving you all kinds of cancer). In contrast, in a nuclear fusion reactor, the vessel wall is the only part that will be bombarded by the high energy neutrons, and if, in the worst case, all the protective layers surrounding the main fusion vessel fail, the neutron radiation will stop as soon as fusion reaction stops. In a fission reactor, the cancer-causing radiation still exists even in the waste materials, which means that extreme measures are needed to burry the waste to keep it as far away as possible from humans. In the case of nuclear fusion, the activated materials (i.e., the metal vessels which have been bombarded by neutrons) can be stored safely for about 100 years, after which the radiation level becomes so low that they can be reused in the fusion reactor again.