In general I think everyone should be able to connect to any instance, as I'm a big advocate of a free and unregulated internet.
But as with many principles there are exceptions, and big data harvesting cooperation are my exception. The idea of the Fediverse is to have a decentralized, free (in both ways, does not cost and libre) and privacy respecting place in a world, where more and more governments and companies start to regulate and decide on what the users can do.
When I look back on the history of those companies I neither like nor trust them, and I think it would be not only a needed action but also a statement when instances defedrate them. We can not stop the data harvesting, as this can be done with simple web crawlers. But with gate keeping (and I do not like it when people do it, but here, I think it is necessary), we can maybe bring the Fediverse more into the public eye. Because when we allow the Threads instances to federate, most people will just see it as Threads. They will not understand what the Fediverse is and will not see it as a new way of using the internet. The same kind of happened with Android, most do not know it is Linux and just talk about Android. I think for Android it is not a big problem, but the Fediverse is a movement, a change and statement people are fighting for, and it shall be and stay that, not just another protocol that is used to transfer likes.
At the beginning of this instance, I once asked the admin and if I remember correctly, a defederation of such instances is not seen as an action to take. Maybe we need to mobilize in other communities on feddit.ch to raise our concern.
(Pinned your post, as I think this is an important discussion to have)