"老美畢竟比較講究人道的"

I don't think this is true. If that were the case, they won't make the whole family based immigration so difficult for greencard holders.

What about all the parents wanting to visit their children in the US but are repeated rejected?

人道?! What a joke.

You got your visa, you are lucky, that is about it. H4 tends to be easier, because they can't be rejected on having immigration intent, not because 人道.