So the discussion around #Tusky is still ongoing. To answer the questions once and for all:
No, blocking something in your software doesn't make it non-free. By definition the LICENSE is not allowed to restrict usage in order to make it free software. The software itself can always do.
Yes, blocking instances is still an anti-feature. By definition an anti-feature is an explicitly added restriction which has no technical reason but a user might act in order to get rid of it.
@sheogorath What else can you do about a software project, which doesn't obey your will, other than calling it names?
Many people still don't understand even that "free" in this case is not about the cost, let alone the distinction between the license restrictions and (anti)features. So why not try and attempt to discredit the project / damage it's reputation, as a warning for others?
@sheogorath It sort of reminds me of the case that OpenBSD project contains an entire paragraph right in the main site's front page, explaining that it's FREE (capitalized) as in freedom, because apparently many people assume it's not (since it's, well, BSD).