I think this is what he's asking:
Say set A is the set containing only the Raze (this), and set B is the set containing all cards in your hand.
Does Raze ask you to select exactly one card from the union of A and B? Or does it ask you to select one of the sets A or B, then select exactly one card from the set you chose?
In other words, does Raze just have you make a single choice, or does it first have you make a choice between two groups of cards, then potentially have you choose a card from that group?
It would matter, for example, if you played Raze as the last card in your hand. In the first case, you'd be forced to trash Raze because there would be a card for you to select from the available options for your one choice. In the second, if you didn't want to trash anything, you'd be able to first select the (empty) set of all cards in your hand and then fail to select exactly one card from it, letting you trash nothing.
You guys are saying it's the second interpretation, but are you sure we know that's how it works? I don't know of any precedent that suggests it works one way or the other. Hermit is the only other effect that has you select a card from two distinct groups like that (discard pile or hand), and it's never mattered how exactly that works because it's optional.