how to allow forum viewing for site visitors, Membership plugin

Can you suggest how to allow viewing of forum topics for a site that is using BuddyPress, bbPress forums and Membership Plugin.
When using Access levels for visitors, it is necessary to prevent viewing of BuddyPress Pages, so this is set in the negative rules of visitor access. However there is no setting for forums, to allow visitors to still view the forum topics.

Is there a way to modify the plugin, or an alternative to still stop viewing of BuddyPress pages for visitors, however to allow visitors to read the forum topics (but not comment on them)?