While I agree there's a huge amount to do, I think it's wise to just find places where plastic use is superflous and visible, and target those first. Now that plastic shopping bags are being eliminated, the next step is to start attacking packaging.
This is a bigger and harder task, but we've learned some lessons and developed some good products in the process of replacing plastic bags, so hopefully we're more prepared than we were before.
I don't have any firm opinions yet. I definitely feel the knee-jerk temptation to not federate with them, but on the other hand I guess federated Facebook products is pretty much what I want from them.
I don't care about Threads very much (at least yet), but I know a lot of people where my only way to get in contact with them is Facebook Messenger. So if I could contact them without needing to have a facebook account myself, I'd be quite happy.