It certainly should not be the intent to always trade away one's 1st rounders. But take the issue of an Aaron Donald. Wasn't he the 11th pick or something like that? So unless the Rams spend a lot of draft capital to trade UP in the 1st round, then they are not in a position to take the Aaron Donald's of the draft.
This is why it seems to be Snead's philosophy that since the Rams are going to be drafting at the bottom of the 1st round, then it is better to take the known players in a trade than to take borderline 1st/2nd round projection players in the draft. Of course this is situational and not a rule.