It's a funny thing and Whirlybird and I have had our discussions on this before; in my experience, I haven't had women say to me "Oh, I couldn't" BUT, Why on earth would I want to!".
There is, (sorry, W) a small age thing here although if I had joined the RAF at 18, I probably would not have been able to fly helicopters. The woman pilot in the RAF who first flew transport aircraft did so when I was about 25.
There was, in the past, a certain amount of nuture and structure in society holding women back but I really do think that this has mostly gone from schools and educational establishments. This under-confidence thing - whilst I accept that it does appear to be the case with many girls/women, I don't believe that social/environmental causes are at the root of this ANY MORE. Times really have changed and think I think there is something within women that is much more instinctive.
As was said on page 1, women don't tend to have an ego; an extension of this might appear as under-confidence.
...and, why do we bother? In an original attempt to answer a question posed by a bloke who could not know the answer any other way. There are some interesting posts on here, not least because some of the women who post here have such different views! I wonder if this is because we are all individual people with our own individual experiences?
Cheers
Whirlygig