Should Journals Have To Compete For Papers?

During the course of the discussions in various locations over the matter of proper formatting of papers for journals, the point was made that in some hard science disciplines (not sure which ones) it is acceptable for authors to submit a paper to more than one journal simultaneously. This is a major taboo in economics, with many journals asking specifically if one has submitted the paper elsewhere when one submits. However, it has always struck me as a bit inconsistent that it is OK to submit book proposals to more than one publisher. My thought on how to resolve this was that book proposals involve the author making money, whereas this is almost never the case for journal articles (although in some hard sciences, one has to pay for pages published in a journal).

I am wondering what people think of this. Should economics journals have to compete for the best papers (and the person who noted this in hard sciences said that this happens)? I can see the taboo arising from the interests of editors and referees. There is already a major problem of finding suitable and willing referees who will get reports back in reasonable time (hard sciences referees also tend to get their reports back much more quickly than do economist referees). Would this make it worse? The argument for moving towards the hard science view is that it is more likely to avoid the problem many young professors face of having their paper sit for lengthy periods of time at journals, only to get rejected, and putting them in danger of not having enough publications to get tenure, even if they have written a sufficient number of good papers.