I think the answer in the article is "So that a Republican isn't."
Clinton's nearly as bad, though. I'm not going to settle for someone I think is terrible just because someone more terrible might get elected. I mean, that's the kind of thinking the general election is for, but primaries are about trying to get the candidate you actually want. Personally, I don't think Hilary motivates her base very well. I don't know any liberals who've said they want her in office.
Oh, I agree, but that's the point Barney Frank is trying to make. Sanders might lose to a Republican, so make sure it's Clinton facing whoever emerges from that melee. I didn't mean to imply that I think that way. I think it's defeatist to think of your vote in only the most strategic/tactical way, especially this early. I want Sanders to be president, so I'm going to vote for him. Barney Frank would think I'm a naive idealogue, I guess!