As a former defense attorney, you should probably be aware that “irregardless” is not a word 😉
First, I’d again like to see the NY or NJ statute, which Joseph claims to have read and assured everyone that it covers Purim. Your constitutional conclusion, while on its face seems reasonable, might not hold up. There is no exemption in the marijuana laws, for example, for consumption on religious grounds. As I’m sure you’re aware, the government can infringe on your religious liberties so long as there is a statute which is narrowly tailored to address a compelling state interest. Controlling underage drinking is most certainly a compelling state interest, and depending on how the statute is written, could be narrowly tailored even if it excludes Purim from the exemption. For example, someone who serves a child to the point where they need to go to the hospital would probably be ill-placed to claim religious exemption. It would all depend on the circumstances.
And again, there is potentially MASSIVE liability under social host law. Potential criminal liability, and even more likely civil liability (i.e., staggering verdicts). No jury will be sympathetic to the fact that “it was a religious holiday” when there’s a kid killed by a drunk driver who was served at your house. Beware.