Some dilemmas describe one effect, followed by an alternate effect “if you cannot” perform the first. In such cases, if the first effect is not performed completely, you must perform the second.
The above quote is taken from the 2e rulebook.
Assuming "unless you [...]" is handled the same as "if you cannot" in this explanation, which I would imagine they are considering they operate similarly, you can't ignore the stopping three personnel just because the choosing a card to discard operation gets bogged down.
The fact of the matter is there's no necessity or penalty imposed for the player who plays the dilemma to choose a card, whereas there is an ultimatum given to the player facing it (Unless you do X, Y happens). In this case, you can't do X (discard that card) so Y must happen instead (randomly stop three personnel).
"Unless you choose to discard that card, randomly select three personnel to be stopped" is a standalone sentence, I don't see how it's linked to or requires a successful "examine and choose a card" operation. You can't perform the action of discarding that card, it's impossible, the only alternative left is to randomly stop three personnel.
This is how I see it at least. Am I correct here?