Why is prostitution not legal in many societies? I'll give a
  possible answer: Wrecks consistency and predictability in a
  social structure. Makes things complicated. Pregnancies and then
  children that have no one to take care of them properly,
  financially and what not.
  *
  Dads or Moms who sleep around with the neighbors aren't watching
  the kids.
  *
  Orphanages are a possibility I suppose.
  *
  Do I REALLY care of it's legal though? Doesn't matter to me
  either way.
  ==
  A society with legal prostitution would need it to be a
  regulated industry. Various certifications like that would be
  required I should think.Might result in dwindling of a nation's
  population which could extinct a smaller country although
  perhaps not a larger country but that's just theoretical.
  Historically, most nations prefer population growth rather than
  population reduction, although we've been in an "Let's encourage
  less population" kick for 40 years now or so. Kinda trendy.
  ==
  *Actually wait: it's not theoretical. The equivalent to enforced
  sterilization is religious communities that are strictly
  non-procreational.The Shakers. Made marvelous furniture. Great
  philosophy. Very modern sounding. Died out.
  ==
  *One of the dangers of legalized prostitution is the illegal
  industries that crop up around it, serving the clientele that
  are not legal. Child prostitution is an income source in
  countries that have poor policing of prostitution. They're sent
  out by the families so that the families can eat. Who they
  choose to send out? The prettiest? The unwanted ones? I don't
  know. But legalized prostitution does run a risk that crackdowns
  on illegal prostitution will not get as much focus and care as
  there are always gray areas that businesses can create through
  paperwork manuveuring, allowing for human rights violations to
  take place. A person who is in a power position in a society can
  choose what to do with their body. A person who is not in a
  power position in a society just has to do what they must.