I think you get the idea he wants to harm her from the fact that he is willing to kill Charlie when Charlie is no threat to him or Claire at all. Hanging someone from a tree to kill them spells mean spirited all over it. Least where I come from it does
There as been a lot of speculation as to Ethan and what his motives were. Just a few points to consider:
We do not know positively that Ethan killed anyone or hung Charlie for that matter. There was a thread a while back that had a mock Ethan trial. It was very interesting. What we know for sure is that Ethan either kidnapped or convinced Charlie and Claire to go with him. Since neither Claire or Charlie remember anything there is no solid evidence either way. Ethan threatened to kill people if his demands weren't met. Sceve was killed yet we don't know any specifics of how that occurred. One thing we do know is that there are many people on the "Island" and it was quite suspicious that Scott didn't correct anyone when they buried Steve and thought it was Scott. I think the jury is still out.
In going along with what you are saying we really don't know who hung Charlie. I would imagine it was more than one person. It would be extremely difficult for one indivdual no matter how strong to accomplish the task. If Charlie were simply tossed from above he more than likely would have suffered a broken neck. Look at the trouble Jack and Kate together had getting him down. IMO it was done by more than one person.