Can We Legalize Pot But Not Prostitution?

Ever since Obama held an online town hall meeting which inadvertently focused on the legalization of marijuana as a tool to stimulate the economy, the issue has been on a lot of radars.  While drugs and prostitution are two very different vices, many European countries have legalized or decriminalized them both around the same time.  So the question follows- if we legalize pot, will prostitution automatically be next? 

I'm not an expert on drug policy, but I agree with a lot of people when I say the amount of time, resources, and energy we spent enfocing drug laws against minor offenders in this country is over-the-top.  The growing amount of money we spend arresting and imprisoning people for minor, non-violent offenses could be much better applied to violent crimes.  But I'm worried that legalization of pot will open the flood gates for the legalization of prostitution and other vices.  Some might wonder what's so bad about legal commercial sex and drugs?  The problem is that legalizing those markets encourages criminal activity like human trafficking, gang violence, and other crimes which are bad and serious.  The fact is that legalization- of pot or prostitution- will have vast ramifications that no one has predicted.     

In the U.S., we more often have separate, decentralized vice policies which range from state to state and vice to vice.  This indicates that lawmakers will see marijuana and prostitution as two distinct issues.  But Europe, the most readily-available litmus test for these sorts of policies, makes fewer distinctions between vices.  Will U.S. lawmakers look internally or externally for guidance? 

Regardless of policy, there is a big difference between buying a joint and buying a human being.