Mission Space IS a very intense ride, if it were not, then nobody would ride it.
It is the general public's demand for such rides that sees the building of taller and faster roller coasters.
Where are the big lines in all the Disney parks? TOT, RnRC, Space Mountain, Test Track etc, etc.
Even so, these rides have an amazing safety record. I read on RADP that 8.6 million people have ridden MS since it opened. I can't vouch for the accuracy of this figure, but whichever way you look at it, one heck of a lot of people have ridden and no one has felt anything worse than sick.
The death of the child is a tragedy and I must admit that I would probably think twice before allowing a 4 year old to ride, but still the most likely scenario is that there was something physically wrong with the child and the intense spinning nature of the ride triggered something that caused his death.
Couldn't the same thing have happened on the tea cups? Or on an aeroplane? Or in a car?
If it turns out that Disney was some way responsible for his death, I'm sure that they will rightly be held accountable, but these seems an unlikely scenario to me.
Every few years someone dies on a ride at a Disney park and it is nearly always down to either some foolish action on their part or due to a congenital disease.
Kev