No, one should not be able to do whatever one wants because this implies infringing upon another's rights, and one should never do that. One must always respect the rights of those around him, both humans and animals, and to have the ability to infringe on those rights with no consequence would be a grave error.
People should be given a certain set of rights, the choice of beliefs, seek happiness, etc. However, they should not be able to do just anything. If someone wants to do drugs and give it to teens should we allow this? Absolutely not, there is a line and keeping people from crossing it is necessary.