Things you should know:
Friendica has recently done away with default comment permissions and has joined the rest of the federation/fediverse in allowing anybody at all to comment on your public posts.
Since this is now practically universal, we've added a new permission role in Red/Hubzilla called 'social-party' with these relaxed comment restrictions. This is available in dev today. If you use your channel across multiple networks and protocols you'll probably want to use this role to be a part of the fediverse party.
I'll probably eventually remove the option for allowing public comments in the Diaspora connector since it's now a standard permission role and otherwise we would need to add the same setting for ActivityPub and OStatus networks.
This is the default privacy mode amongst all other projects in the fediverse. If you use one of these networks, you can't change it. You can only block people after they spam or harass you. It is actually the most permissive of Hubzilla's four social privacy roles, and we would encourage you to use something a bit more restrictive - but we believe in giving you control of your privacy. We can not and will not force you to accept a network privacy policy.
If you choose a more restrictive role, your privacy takes precedence; even if the other network doesn't support it. If you only allow friends to comment on your posts (standard in our other privacy roles), anybody in the other network will still see a comment box and they can submit a comment (because their network allows this), but unless they are a friend of yours you will never receive it. This is unfortunate, but until these other networks actually give you control of your privacy, it is something we have to live with.
And if you don't like any of our standard privacy roles, you can always make up your own (either more restrictive or less restrictive). There are a few million possible combinations.