Can I comment in a nation I'm not a member of?
Yes. There are three Nation types: Open, Gated, and Invite-Only.
You can leave comments in Open and Gated Nations without membership.
If you're not a member of a Nation that you can comment in, you'll still see the same 'Reply' buttons that you'd see if you were a member.
If the Nation is Invite-Only, and you're not a member, you won't see a 'Reply' button at all.