Evolution cares more about survival than anything else and puberty is a key part of survival. By forcing the body to halt or slow the normal processes causes damage to the body. The more intervention by people before the process is complete, the higher the risk of damage to that system because puberty affects the entire system not just the sex organs.

The body needs to complete the normal process to a certain point to lower the risk of perminate damage. Suicide is one extreme but what about those that aren't considering suicide but would be willing to take the drugs. We would probably see a measurable increase in debilitating deformities and life threatening illnesses. Should anyone give someone the option to make this choice when that person isn't even mature enough or experienced enough to make such a dangerous decision.

Once the decision is made it can't be taken back, the risk out weighs the benefit.