The only reason a turn downwind at low level is dangerous is because many pilots in this situation try to maintain a constant groundspeed ( this is natural because they are looking outside not inside at low level so they don't bump into things).
So from 40 kts IAS into a 20 kt wind, the pilot turns downwind (subconciously adjusting attitude to maintain his 20 kts groundspeed) and suddenly finds himself with 0 kts IAS, no translational lift and a descent because he hasn't compensated with extra power for the loss of ETL. Oooo...low speed, RoD and power applied....we know a song about this don't we children? It goes: vortex ring, vortex ring, vortex ring; vortex ring, vortex ring, vortex ring. (In a football chant sort of way)
This is demonstrated to all Britmil helo pilots to highlight the dangers of manoeuvring at low level in windy conditions and to underline the need to constantly cross refer to instruments.