I think the barrier is there to prevent small,ill equipped aircraft with unskilled pilots getting in the way of the more professional well kitted aircraft.
I've just been flying here in Asia today on a 550 miles round trip where we flew at around Fl 22.(Pressurized Malibu Turboprop) Just a 2 hour jolly.
We descended on track/time from 15000 ft to have to hold for several minutes
because of poor track/timing by a C150.
Annoying to say the least when we could have parked and had a coffee while a
poorly managed ppl got his act together
