The letter writer doesn't affix labels because he uses the SPLC to do so for him.  SPLC has repeatedly labeled pro-family associations as "hate groups" because they oppose, through lobbying only and not violence, parts of the LGBTQ agenda.  Standing up for privacy in girls' locker rooms is a hate crime to the SPLC.

SPLC teaches tolerance only for those they agree with.  Not so much for everyone else who is not on board with the agenda.