Air carrier First Officer reported a NMAC with a helicopter that crossed in front of them while on approach.

Narrative

Inside of the final approach fix on the ILS 32 into PIT ATC cleared a medical helicopter across the final approach path which eventually led to a pass well within 500' of our aircraft. ATC informed us of the helicopter and we made visual contact but the distances involved were neither safe nor necessary. We anticipated an RA and were primed to initiate a go-around as the helicopter crossed in front of us.ATC had plenty of options to avoid this situation; including slowing our aircraft early; vectoring us to arrive on the final approach segment later than the helicopter; or simply not clearing a helicopter to fly across a final approach course while an aircraft was inbound. They could also have ordered us to go around. While we called the traffic in sight" and ATC ordered us to maintain visual separation; it was a significant and sudden burden to place on an airliner already in landing configuration and while we were already in very close proximity to the helicopter and headed for an unsafe pass.On reflection; our crew may have relied on the TCAS system to determine if the closure rate was safe rather than executing a go around in advance of an actual RA as we became aware of the situation; but the combination of darkness; dramatically mismatched speeds and surprise made the final separation difficult to gauge. We believe this error to be largely caused by poor decision making by ATC. As is the case with so many automated systems that are meant to relieve pilot workload or bolster safety; TCAS should not be relied upon to determine if closure with traffic is safe in lieu of pilot judgement."