I saw it more as an equality issue...if I wasn't going to lend much credence to "please promote me" letters, then I wanted to give equal weight to ""DNP" me letters...in other words--give all letters to the board equal weight. Comparing it to an SIE from UPT is like apples to Tuesday, though. A promotion board is not charged to find the best records "of the willing"...but is charged to put the records in order, best to last. IMHBAO, a member's opinion/desire for promotion isn't very relevant to how well the RECORD stacks up against other RECORDS--even for the purposes of promotion. For DNP me letter writers, if it were possible, I suppose it would be OK to specifically request your record NOT compete for promotion at all. But that's not how our system works. Maybe it should--that WOULD ensure we're only looking at the willing.
To me the officer's performance, as recorded in OPRS/DECS/PRF (in that order) are much more relevant to determining the "quality" of the record. Also, specific SECAF instructions to the board play into how the letters are treated....and how individual officer traits are treated.
There are never very many letters to the board. This isn't a widespread issue, nor a big deal for 99+% of officers meeting a board. It's a HUGE deal to each letter-writer, though...and every letter was read (some several times, because they were tragic, or long, or just interesting examples of the varied human condition)...and I gave every letter I read equal weight in calculating the score of the record. So they weren't disregarded. Just not highly regarded.
I don't recall being surprised that someone with a "DNP me" letter made the promotion list. If it happened, then that officer still has options: take it or not. Circumstances change. People change their minds...some who are promoted won't accept, or will wait until pin-on day to reject it. Some who thought they WOULD be promoted won't be, and will make choices based on that. Some 5APZ dude with a P who thought promotion was never gonna happen gets the nod and has to make new choices based on that info. Some "DNP me" letter writers may change their minds in the months between letter and list release and pin-on. What we should NOT do (institutionally, as a SERVICE) is accept a "lesser" officer for promotion in lieu of a "better" one just because the "better" one doesn't want promotion, or because the "lesser" one made a really good argument for promotion in a letter. We should promote neither. And I'm pretty sure that's what happens in the vast majority of the incredibly small number of letter-writer cases.