This guy is a Professor in nanotechnology with a few impressive awards and administrative positions for his accomplishments in the field.
He has devoted his work to bettering the plight of mankind in resolving some of our grandest challenges related to climate change in general and how applied nanotechnology can help us build useful materials in particular.
Furthermore, he wrote a decent book with some useful information and references despite of his poor final conclusion.
So, while he may be wrong on some things he certainly is not "an enemy of mankind." In fact, such ridiculous statements have often been used to first dehumanize and then abuse a variety of people throughout history. And justify hideous crimes against humanity.
If you want to be intellectually honest and disagree with someone put forward an argument against them rather than a personal and ridiculous attack on them being "an enemy of mankind."
This is what the Church did in order to justify burning at the stake the best and brightest people during the dark ages. It is a convenient yet most dangerous and intellectually lazy and dishonest of paths.
So, if you look at history, usually those that have called others "enemy of mankind" have historically turned out to be exactly that.