As pointed out by @lizrice the flag might be ambiguous:

• If it means "who can verb resource in any namespace" then yes, I think we should be looking at all the possible rolebindings.
• If it means "who can verb resource in all namespace" then we could limit to just clusterRoles, but then we'd be missing the possibility of someone who has this ability, not through a clusterRole but by being bound to a Role for every namespace

The first of these options seems more useful anyway. Either way, we should clarify it in the usage.