Motocross is a dangerous sport but you can minimize your risks by wearing the proper safety equipment including a real neck brace, not just a rubber donut. Also, you must be physically fit and in good practice before really competing in an organized event. I have raced since 1975 and have broken many bones and have herniated discs in my lower back. I have two areas of metal bracing in my body but I still compete as often as possible.
Most of my injuries came from not having enough impulse control and riding above my abilities or just dumb luck like having someone land on my back on the landing of a jump. I am glad my sons don't race as it would make me nervous to watch them but I dont worry about myself in that way.
For me the risks are worth what I get out of the competition, staying fit at 53 years old, keeping the mechanical aspect in control and enjoying the comraderie of the other old bucks chasing the dragon.
with free style motocross being more main stream, no one thinks MX is extreme anymore.