So, there are basically three (technically, four) voting options:
1) For (opt out)
2) Against (same as #3, as in do not opt out)
3) Abstain (same as #2, as in do not opt out)
4) Refuse to vote (which is effectively the same as #2 or #3)
Therefore, it's essentially only two choices: opt out or do not opt out, and the board conveniently doesn't provide a recommendation because if they did, retail shareholders would know to do the opposite of what the board recommends. However, by not recommending anything, the board is by default recommending inaction (or #4 which is effectively the same as #2 or #3). Ergo, I'm assuming the board doesn't want retail shareholders to choose #1, or opt out.