Sure. I thought that had been explained adequately in this thread, but possible risks of IWR include:
1) Oxygen toxicity
Yes, this is a risk, but I don't see how managing the risk of oxygen toxicity during IWR would be more complicated than managing the risk of DCS from multiple dives in a day. In both cases, you simply need to keep track of how much of the gas (either O2 or N2) is likely in your system based on your dive profile and surface time etc. If we think divers are responsible enough to follow a table for nitrogen, then why can't they similarly follow a dive table to prevent oxygen toxicity for an IWR recovery? And if the diver has a table, or a computer, or even a simple rule of thumb for a time/depth that's highly unlikely to risk oxygen toxicity, then I don't see how this is a reason to not attempt IWR.
2) Loss of consciousness underwater due to DCS or seizure
I don't have actual knowledge about this, and would like to get a better understanding of the actual risks of that. I think the debate around the general soundness of the concept of IWR really comes heavily down to this point.
Based on the fact that DCS symptoms are often reported to get worse over time, I would hypothesize that it simply takes time for the nitrogen bubbles to burst free from blood/bones/etc, and that if you go back down at the earliest sign of symptoms, then it will prevent the remaining nitrogen in your system from escaping and give you time to equalize to a more normal level of nitrogen while under pressure.
Thus, if my hypothesis is correct, then symptoms of DCS would only continue to get progressively worse (ie, into loss of consciousness, seizure, etc) if you remained above water, in which case the potential worsening of symptoms would be a strong argument for IWR, not one against it.
Of course, I'm not a medical expert, and my hypothesis here could be totally wrong. Perhaps all the damage is done immediately upon surfacing, and the progression of symptoms is already set in stone from that point onwards, so that it makes no difference if you go back down under pressure. If this is the case, then it's a strong argument against IWR in any circumstances.
Are you aware of any evidence to suggest that this hypothesis is correct or incorrect?
Considering that IWR must be performed at a shallow depth, shallower than the actual dive that was just completed, the diver must already be wearing (or have available) exposure protection that is at least adequate for this depth, so I don't see how this is a reason not to do IWR.
4) Lack of ability to aggressively hydrate
We're talking about less than an hour, I feel like the risk of dehydration from not drinking for an hour cannot possibly be significant in comparison to the risk of not immediately treating DCS, so again not a reason not to do IWR.
5) Delay of medical care in general if the diagnosis is incorrect (e.g. pulmonary barotrauma, stroke, immersion pulmonary edema, etc...)
Worsening of the diver's condition if the diagnosis is incorrect (e.g. pulmonary barotrauma, stroke, immersion pulmonary edema, etc...)
That's certainly a valid risk, and could be a reason not to do IWR, but this could be overcome with better training at identification of symptoms.
6) Risk to the support divers
There is always a voluntary risk taken when diving recreationally, or when voluntarily participating in a rescue. If IWR is considered to be a potentially life saving procedure, then that's not really a reason not to attempt IWR.
Again, we are probably in agreement that IWR should be done in SOME situations. Very few people would say that it should never be done, so that's a straw man. The devil is in the details.
I honestly don't feel confident saying that IWR should be done in any situations. I have a hypothesis that it is, but I'm not confident about that yet, largely because I don't have factual proof of my hypothesis regarding your point #2.
A person who is showing no signs of DCS is considerably different from a person showing mild signs of DCS. Mild signs of DCS can progress, and they can progress quickly. If no signs progress to mild signs, then you have changed categories and should act accordingly.
A friend of mine surfaced after missing some stops (the circumstances would take several paragraphs), and soon after surfacing, he started to show mild signs of DCS. While he was still in the water, people assisting him from a boat put him on O2 from his decompression bottle and brought him to shore. Once on shore, he was able to assist in getting his gear off and preparing for his evacuation. He started to show stronger symptoms as they prepared to leave. A few minutes after they left, the paralysis from the waist down set in. It would not have been good for him to be going through those stages under water. Perhaps if they had had the equipment needed for truly effective IWR, it might have been different, but they did not have that.
Thank you for sharing this story. It really relates back to point #2 above though -- and if my hypothesis is correct, could actually be a case for IWR, rather than a case against it.