...using that post, without making it clear to other users that the post was originally written in another thread, in another context?

I feel this is grossly unfair for a number of reasons:
- The original post may have been made in response to a post, and the context is lost when it is reposted.
- If other users don't know the post was originally made in another context, the thread may appear more antagonistic/out of proportion/dualistic than it was originally intended to.
- Many users are uncomfortable about starting their own threads and don't usually do so. It could be argued that by placing users unwittingly in this position, the mods are acting in a way which could be received as punitive or shaming.
- Some users feel 'safe' staying within a particular area of the site, where they experience friendship and support from other users. Moving their post to another area of the site may be hurtful for this reason.
- By putting someone's comment up for debate in this very public way, the OP could feel "shouted down" in a platform they are not comfortable engaging in.
- It is simply misleading for everyone, if such a practice must exist on this site, surely users should be made aware of when it is happening.

Personally I feel the mods have a certain duty of care to users of this site (particularly the owner) and I feel that acting in a way which a user may experience as shaming is grossly unfair and potentially unethical. Why not speak to the user in question and give them the option of starting a thread if they wish to do so?
Also would it be so hard to inform other users that a certain thread was a originally a post from another thread, and posted in a different context? These seem to me to be very simple steps to prevent a user feeling hurt or misrepresented.