Board Thread:Suggestions forum/@comment-34241117-20180207232730/@comment-29773086-20180208184551

Some of the Haradrim may have not exactly willingly followed their Dark Lord- but they would still have been brought up in a Haradrim society, and taught to hate their enemies and fear their lord. They are still evil Men, and as such the good-sympathetic narrative is not quite right either way. And by no means would all the Southrons be glad to be free; many of them were fanatical followers of Sauron.

There's no honour in killing a merchant, you're right. The Rohirrim wouldn't kill him to gain honour, but to stop enemies from trespassing on their lands. At best they would capture, question, and imprison him. Either way they would not help him along on his journey.

The Ents are likely to know of the Haradrim. They have travelled widely in search of the Entwives, and could have easily visited Harad. But whether they have or not, on a quick questioning of the captive, they would find out that he served evil, and would probably kill him, and at the very least remove him from their forest.