The irony of this thread is that all the responses to CM have about the same purpose as the letter on OO quoted in the OP. Namely, the supposed target of the arguments can never and will never appreciate or understand their gist. The purpose though, is to have the answers yourselves.
On that note, I will throw a few more words into the mix. It is impossible to deny that behaviors and customs practiced by Orthodox Jews have changed over the centuries. Some changes are innocuous, such as declaring a focus for avodas hashem to be through emotional religion (chassidus) vs. through exclusively talmud study (litvaks). Such changes may be very easy to see and topic for endless rivalry, but at the core nothing is changed before and after (or from sect to sect). Other changes have been fundamental, such as Hellenization and Reform, which in hindsight (if not at first sight!) were clearly movements to undermine basic tenets of the Jewish religion. The above letter serves to categorize OO in the latter group.
