Josh wrote:2. Our society doesn't associate having hair up with modesty.
At one time, the bulk of our society would have thought that women should either have their hair up or covered in public in order to be modest. Long flowing hair was ok in family and in lady friend settings but not in public.
I'm not saying by this that business partners today should expect women to adopt this practice when they show up over lunch time at the place of business, but just trying to show that our American collective conscience on this matter has changed.
Josh wrote:4. Plain people really think women should wear their hair up. They don't feel the same about covering one's feet, so this is clearly just a cultural application of modesty.
Possibly, however people did not cover their feet in the Bible times, married women did veil their heads, and there is no indication that this was out of order.
Josh wrote:5. I am wondering how expecting a woman to have her hair up helps spread the message of the gospel.
The assumption of plain people (and many Christians in the Mid East and eastern Europe) is that women should cover their hair or hide their glory while in public and that there is value in doing so and that there are blessings associated with making this a part of one's culture. The underlying assumption is that this can (not will) contribute to good men / women relationships in a society over multiple generations.
The same could be said for living in community, giving children a Christian education, being able to sing beautiful songs, etc. It takes a long time to build solid stable culture and some things do not show their benefits immediately. Those who are looking for immediate results or looking for a scripture verse for every thing they do are going to miss a lot of things that only come with the development of a Christian worldview.
For the record, I do not say this to say that the way your acquaintance handled the long hair thing was a good way of handling it.