Saw that letter on the web about a year ago, complete with the biblical references... What a frightening book both the Old Testament and its Jewish original are, and what a worry it is that some people think that such ancient guidelines can apply today. I have no problem with the 10 commandments, but to consider that it is a mortal sin to sew your buttons on with a different thread, or practise birth control...
The other worry is that so many extremists of every stripe can accept SOMEONE ELSES interpretation of any sacred book, instead of reading it for themselves and letting common sense percolate.
Maybe they are extremists BECAUSE they have no common sense.