> ..not that all of these share federated auth. You can not “sign in” on any other server than the one you registered with.

Oh definitely, I haven't conflated the two. The issue (at least for me) is I haven't found a way to limit mass propagation of content. Things I post in one federated instance may not jibe for others when it is a two-way street. Vice versa, maybe I don't want the exposure from more radical persuasions and/or content. Trying to reconcile the tradeoffs is also an issue in of itself as well.