'Legitimate' is too broad. Google defines it as: 1. conforming to the law or to rules. 2. able to be defended with logic or justification; valid. Definition 1:

'Legitimate' is too broad. Google defines it as: 1. conforming to the law or to rules. 2. able to be defended with logic or justification; valid. Definition 1: maybe, although even that may be borderline, since these unsubstantiated suits sound pretty vexatious (IANAL). Definition 2: no way that this is justifiable, or that this peculiarly broken aspect of the US legal system — where you pay your own costs even if you win — can be defended with logic.