Yeah great safety at this not, a flimsy plastic fence is all nothing substansial between the cars and the crowd if it goes wrong, got love the lack of health and safety though.
As can clearly be seen if one of these D1 drivers lost control there is enough people standing at track side to slow the car down as it hurtles out of control off the track.
The plastic fence is not there to stop the cars it's merely there to provide the crowd with something to stand behind so they dont venture onto the actual course and get in the way.
You can clearly see in that video that the car slowed and stopped very quickly once it ploughed into those people, the crowd serving their purpose exactly as intended. Crowds of people are perfect for slowing out of control drift cars and offer alot less damage to the cars than a concrete wall would according to what the japanese safety crews at D1 demos in Tokyo auto salon think.
I don't know why this is becoming a point of debate about the safety of the spectators. Ever been to a rally event? Baja 500? King Of The Hammers? No fences, railings, walls or anything else to slow a vehicle before it plows through a crowd of people. No one makes these people stand there. They choose to.