There is absolutely no evidence that junior staff are "stupid".
However, there is plenty of evidence that young workers are more vulnerable to workplace bullying, harassment and intimidation.
Young workers deserve respect in the workplace. Young workers have a right to work in safe environments. That's why we unionise.
http://www.theage.com.au/small-business/trends/the-big-idea/why-are-junior-staff-so-stupid-20151201-glchss.html