I view it kinda differently because that public post is still there (with the creators consent), and you can naturally run into it if you're a member or interacting with that group. However, this is a re-post and specifically a group targeting them as negative which can lead to brigading.

I definitely understand public is public, I think it's more of an ethics/moral choice where anyone wanting to harass the user would have to take extra steps since the information wasn't provided by this platform.