Joseph,
You were absolutely positive, until 20 minutes ago, that social host laws didn’t exist. How can you still maintain with absolute certainty that Purim is covered? Wanting doesn’t make it so. The woman in the article would not have been arreste with the call to the police. How do you know the same thing wouldn’t happen if police are called to a yeshiva Purim celebration and found significant amounts of alcohol being served to minors?