Why is it difficult for parents and children to talk about serious questions?

i think that the reason for this is because the parents are actually scared to find out bad things about their children and they want to believe that their child is doing the right think. its like the dont ask dont tell motto

Those topics are easy to discuss for everyone, so with parents and children it's even harder. Parents tend to get protective and think that the best thing they can do is to keep their kids as far away from those things as possible...and some of them think that if they never talk about it they won't get to know about it, which is often untrue because they will find out at school, with friends etc. We're biased by our own prejudices, so are parents.
Anyway i disagree with one of the things you said: parents shouldn't try to be as equals with children. They can be open yes, but parents cannot be their kids' friends, parenthood and friendship are completely different and there is a point of authority that must be mantained all the time.

Most parents found it hard to accept their children's attitude.They themselves had been to respect traditional values.When they come to teach moral values,they always are teaching their children exactly what they had been tought by their parents.Even it is not the things of the past and will be right now,but that seems no suitable for the trend of the times.That is the reason.