I fairly regularly get users that are confused on how to comment on a forum, or create a ticket, and they can't figure it out since "Create Ticket", etc. links aren't even shown if you don't have the proper privileges.
I think it would be best to show always the "Create Ticket" link (or create thread, whatever is appropriate per tool), then show them what privileges they need if they don't have them (or just punt them to a login page if that's all that's necessary).
For locations with discussion, show "login to comment" where the comment box would be.
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