The content of this letter is nothing new. The writer has an axe to grind, and so the letter is sent to newspapers where, given their own politics and inability to filter out bigoted hate speech properly, the woman is given a forum for her hateful views.
I suppose there is a benefit to this. Without the publication of these letters, how would you know who the crazy people are?
But the very idea that someone would get to say "homosexual marriages" are "based on something that is morally rotten so they cannot serve to promote the good health of our society" is to promote the ideas of a world class bigot. That is what is morally reprehensible here; not the fact that gay people want to be married but that some crazy lady in New Ulm, Minnesota would get a place to spread her eliminationist rhetoric.
Mary Thom claims to not be "extreme" but that's what she is--an extremist who wants to destroy homosexuals because they are morally rotten.
What's moral? Hating people? Hating the way they were born? Hating the way they live their lives?
When someone says "we cannot afford to be tolerant" it means that being intolerant is perfectly fine. From that, we see violence, shootings, hate speech and murder. We see people assaulted, killed, attacked, shot, knifed and stoned to death.
Someone let Mary Thom emerge from the swamps of cruelty and viciousness. Her letter should have remained there.