If we mandate that some offenders have their behaviors controlled by drugs, we are trading civil liberties for security.  We are infringing on the basic human rights of the offender in order to reduce the danger that the offender poses to our community.

In general, people have the right to live their lives as they want, without the government trying to control them in very intrusive ways.  The government has the right to prohibit certain acts (crimes) but it does not have the right to do invasive things that would prevent us from being able to commit those acts.  For example, the government has the right to prohibit people from acting violently and to punish people who engage in illegal violence.  However, it does not generally have the right to do something like forcibly administering drugs to all young men to reduce their violent tendencies.

When we control offenders using drugs, we are breaking the rule discussed in the previous paragraph.  We are forcing offenders to give up some of their agency as human beings.  This is a serious violation of civil liberties.  On the other hand, we are making society safer.  We are controlling people who have shown that they are capable of illegal actions.  We are also allowing them to return to the community so long as they submit to controls.  This is, in a way, good for them because the alternative might be to incarcerate them permanently. 

This, then, is our tradeoff.  We are allowing serious infringement on civil liberties in return for making our communities safer and allowing offenders to reenter those communities.