The question why rich countries should help poor countries is based on hunanitarian principles.
问一下，why 能否改为that呢? 说它是同位语从句句意也说得通啊？
The question why rich countries should help poor countries is based on hunanitarian principles.
我感觉可以把why 改为that！
我学校的内部语法书上在讲表语从句时有这么两句：
The reason why he has been such a success is that he never gives up.
他获得这样成功是什么原因因为他从不舍弃。
The reason why he did not come to the meeting is that he was ill．
他没参加会议是什么原因因为他病了。
参考译文：
为何富国应该帮助穷国的问题是基于人道主义原则的。