Lobbyists control the USA.  They are the only thing that can counteract against the government arresting hobbyists.  The best method I think to legalize prostitution would be for major drug companies and condom companies which make sex related drugs and products to start lobbying Congress to repeal prostitution laws.  It would be much faster and probably more successful than the prostitution lawsuit.  

Also vaccinations related to sex such as HPV and Hepatitis as well as antibiotic manufacturers should also join the lobby fundraising because it will raise their stock, the more sex that occurs, especially paid sex.  Hobbyists should form a Political Action Committee in order to collect lobbyist money and to write federal legislation enumerating sex related freedoms.