IIRC, we were fairly unaware of the long term effects at that point. All we really knew was that age had a factor. So a bunch of healthy young people would have

IIRC, we were fairly unaware of the long term effects at that point. All we really knew was that age had a factor. So a bunch of healthy young people would have signed up, thinking that the chances of harm, even if they got the placebo, were fairly low, when in reality there were significant chances of being permanently (or at least very long term) maimed. Essentially, no one signing up for the trial would have been properly able to give consent, because no one knew the real consequences.