I think that - as in most things in life - experiences vary. For every woman who's delivery is 'compromised' by her partner's resence, another finds her experience is enhanced - there are simply no hard and fast rules.
I was present at the birth of our youngest daugther, and was very glad i was - and I know my wife was glads to have me there as well.
It is a matter of personal experience, so the professor's words will strike a chord in some readers, and appear as nonsense to others.