Fifi read your comment back "for me personally I don't think my ex being there would have made me stress out just how I was in my birth I was very calm!"
They are statements about you. You kee psaying 'how do you know X' about the man. Well how do you know the OP will be the same as you? How do you know she would be comfortable wearing a long shirt? Why should she have to protect her dignity whilst in labour?
You say you understand how labour works because you've done it four times, So why are you not understanding that stressing a woman out in labour IS dangerous and at the very least horribly painful.
Being on your fourth pregnancy i am assuming you have experienced cramp? Cramp occurs when set of muscles goes wrong, and they both either shorten at the same time, or lengthen at the time time. Now, putting stress on it only worsens it. They need to work together so that one shortens while the other lengthens.
This is in basic terms how the uterus works when it contracts. Putting stress, in this case the automatic physical reaction of tensing (And the reason such techniques as massage, deep breathing and using water are helpful) essentially does the same thing as cramp does.
This prevents the cervix from effectively opening - Which can lead to fetal distress amongst other things - and can place pressure on certain parts of the baby as well. Not to mention problems with positioning that can occur if a mother is unable to labour effectively (Most women automatically move to optimal position depending on where their baby is, to allow baby to move down properly). There are too many problems to even list.
I don't understand how you can claim to understand how labour works yet insist it can do no harm him being there against her wishes just because you weren't stressed.
My ex was present at my birth and was fantastic BTW, I'm not biased. He was there because i was confident he could support me effectively as far as telling me what i want to hear, holding my hand. I did have a friend present too because i knew damned well i couldn't rely on him to argue my decisions if i weren't able to and i have certain medical beliefs.