Air carrier Captain reported a NMAC (near mid-air collision) with an opposite direction helicopter at SDF. Crew executed RA profile and went around; after which ATC advised the traffic was a helicopter who had them in sight.

Narrative

During a nighttime ILS approach in VFR conditions to Runway 17L in SDF; we got a TCAS RA. We were descending on the glideslope; Autopilot on; and approximately 1200ft AGL when a TCAS informational target popped up to the right of the aircraft - about 600 ft low and less than 2 miles away. This is not too unusual for airports with closely spaced parallel runways; but when I checked the Cockpit Display of Traffic Information (CDTI) for more information; I found that the traffic was not paralleling our course; but moving towards us. Its path would cross ours right to left; and the targets would merge. Around this time; the Tower attempted to contact us. In just a couple seconds; the TCAS went from nothing; to non-threat traffic display; to TCAS RA. We followed the TCAS instructions; which led us into a go around and a return for a second approach and landing. At the closest approach; there was less than 500 ft vertical separation from the other aircraft with targets merged on TCAS.During our go around; the Tower said that the traffic was a helicopter; and had us in sight. As you might imagine; this did little to reassure us. I am appalled that this continues to happen. It is a dark joke that 'Regulation is written in blood'; but it is also oddly reassuring. Knowing that as an industry we are committed to not repeating the mistakes of the past. But something is unfinished here. This should NEVER have happened.Cause:I do not know where the original mistake was made; or what the control structure is for helicopters in that area. I assume that the airspace that close to the airport is under the control of the Tower. I also do not know what instructions were issued to the helicopter pilot. But I do know that helicopter traffic mixing with landing traffic is a clear and deadly threat to safety. I know that visually judging distance between aircraft at night; with the accuracy needed to maintain a safe distance under these conditions; is so difficult as to be impossible. A 'maintain VFR separation' clearance should never be issued or accepted in this situation. I know that helicopters should never; and have no need to; cross the flight path of an aircraft. This is the whole nature of a helicopter. They do not have to move forward in order to fly! I know that the quick reactions of my First Officer; the pilot flying; helped prevent another tragedy.During this event; the 'startle factor' was very high. We had no idea that there were any traffic threats between us and the airport. That knowledge would not have changed any of our actions pre-TCAS RA; but it would have made the recognition and safe resolution much smoother. That zero to 60 moment of no knowledge; recognition; and action is a hazard in itself when seconds can be a literal matter of life and death. One thing that contributed to this lack of information was a late transfer from Approach Control to Tower. The instruction to change was given at about a five mile final. This is also the place where we are typically running the Before Landing Checklist. Because the instruction came while we were running the checklist; we had to re-run that checklist. This led to not having checked in with the Tower when the traffic first popped up on TCAS. Given our duty to Aviate; Navigate; and then Communicate; and the common situation of having to wait for a chance to communicate with Tower; I recommend that the instruction to switch to Tower be given farther out on the approach. But once again; this would only have lessened the startle factor. It was not a primary driver for this event.I have been doing this job for many years; and it is hard to avoid the feeling that Tower Controllers are trying to push traffic separation responsibilities onto pilots; while creating situations that actually make that harder and less safe. High performance aircraft; crowded traffic conditions; poor visibility; restrictive ATC instructions. All these things push 'see and avoid' into impossible territory.But it is relied on every day to improve the flow of traffic; and make the controller's job easier. It is only the invention of tools like TCAS that has made aviation's incredible safety record possible under these conditions. But these tools were made to solve a problem; make the operation of that time safer; not to make it possible to squeeze more traffic into the same space with less oversight.