"In other words, the dispersant use is experimental; it smacks of doing something that may be no better (or may be worse?) than doing nothing".


Maybe yes, maybe no.

Before EPA let BP use dispersants at source (as opposed to the ineffective air spraying of weathered oil), they had to be proven it disperses the oil....as no one knew if it would be effective.   That was proven to be so....check out the science reports on the effectiveness, near and far field.

A significant amount of the oil was kept from the surface (aka the plumes)...allowing the workers to work in a safer environment, and reducing the amount of oil reaching the surface (where it could do more immediate harm to surface species) and on the shores and sensitive wetlands. I suspect a trade off for the lesser of two bad situations.

Q, none of those statements or links you provide show much that is new, nor unknown. The environmental impact of dispersant use (any of them) in such a large spill (like a major oil spill every day), and in such deep waters is not modeled, studied mor known.

But, that alone does not rule out the other reasons for using them that I noted. If, at a minimum, they are no worse environmentally than the oil without dispersants....the other reasons for their use (protecting shorelands, wetlands, limiting the surface spread and specied damage....along with protecting workers safety) makes sense to me. For the vast amount of oil released, a surprisingly low amount (IMO) has reached shorelines.....and there were long periods where no dispersants were applied at source.

During Exxon Valdez they steamed cleaned shorelines, when it was known that it did more harm than good (killed the beneficial bacteria), possibly to show the public they were doing something.

At least, in this case, scientists were consulted and a measured decision was made based on the greatest good in a tough situation, where spill technology and science has never been before.

Was it the right decision? Time will tell.