> I'm not sure where the line crosses between mental illness and just bad behavior, if there is a line at all.

yeah. this is currently the subject of much debate.

> As much as I believe in help for the mentally ill, I also believe that people who are dangerous--for whatever reason--to the general public, need to be taken of the general public.

Yeah. institutionalisation the answer to both.

When people have offended we can lock them up in jail against their will.
When people haven't yet offended but we think they are likely to offend we can diagnose them with something and lock them up in a mental institution against their will.

Some people argue that psychiatry (when used to involountarily commit) is a form of social control that picks up where law leaves off. Whereas the legal aspect relies on their HAVING OFFENDED ALREADY the psychiatric aspect relies on clinical judgement about the liklihood of FUTURE OFFENDING.

but its ok because people in the latter group are 'defective'.