What the hell are you even talking about?

A post in a publicly accessible forum is a billboard on the highway. You put it up and anyone can read it. You have zero expectation of privacy after having done that.

Changing the speed limit on the highway ("Rate Limiting") in no way affects the fact that you put up the billboard on the first place. People may be driving by a little slower, but they're only reading what you chose to present for them to read.

Scraping does not infringe on privacy. The privacy infringement is that you made the post in the first place. Under normal circumstances, you are the only person at all capable of infringing on your privacy. Exceptions would be someone spoofing your credentials to create the post without your authorization, but someone who does that victimizes both you and the forum hosting your post.

What you're talking about is more closely related to intellectual property protections like copyright. A musician can play their song over the radio without surrendering copyright protection. Nobody else can make (commercial) use of that song just because it has appeared in a public space.