Meta can see any public posts anyway, because they are public: all they need is a web crawler, which they have.
One of the dangers in my view is the extra costs of federating with Threads, which can make running small instances unaffordable, and promote consolidation of the user base into large instances.
Thankfully, entire instances can be blocked, and I anticipate that many will block threads.net as the means to block not only the shenanigans from Meta but also to survive as a small community and on a limited budget for running the server.
Even individual users can block entire instances in their Preferences, under "Import and Export", "Import" tab, choosing "Domain block list" as the type of CSV file to upload – and all the file needs to contain is "threads.net" without quotes.