This man who supports Extermination of Gays should not only be denied entry to the United States, but should also have any/all US Passport or Visa rescinded.

Any PM from ANY country that supports extermination of an entire group of PEOPLE should have ALL SUPPORT by the United States rescinded.

A Concerned Citizen of the UNITED States of America.

If a visa is tied to a specific event the authorities usually require a letter from the event managers (and something beyond an email). The event managers have disavowed this. The other option is that he put down the conference as a reason for the trip but the visa was not tied to the conference (any legitimate reason would have done). Personally I would let him come and see who he talks to.