Why should the scientific community avoid double submissions?
One possible answer is that the referee process of a paper is a very professional and time consuming job (at least I am sure it is in mathematics). Therefore it is not fair you submit your paper to several journals and make them to referee your paper by different experts and then you withdraw your paper just because your paper got accepted by another journal.
I think there are three reasons.
- From the publishers' perspective they want to squash competition. They want to know that if they invest the time and resources to evaluate the paper that they have a very good chance of publishing it. I don't particularly like how the publishing industry currently works and I might argue that this is in fact a reason to double submit.
- The second reason is about the reviewer and editor resources. These are our colleagues and wasting their time is not fair. As a reviewer I want to know that if I put time and effort into a review, that my comments will be considered. Even if my review leads to a rejection, you will likely think about the feedback before resubmitting.
- Having little or no cost associated with multiple submissions reduces the effectiveness of the peer review process. You increase the chance of finding a set of reviewers who miss flaws and potentially ignore reviewers who find flaws.
If the point of publication was to get it published as quickly as possible, then there might be some merit to your argument. But the point of peer-reviewed publication is to have the community vet your work and certify its basic soundness (not value/impact necessarily - that's a different story).
In that case, the delay involved in publication is a problem that needs to be fixed, but you shouldn't fix it by allowing multiple instances of peer-review.