It isn’t an unstated purpose; its perfectly overt; and perfectly necessary since the alternative is to surrender unlimited power over our lives to capitalists.
The difficulty arises in part because a fairly large amount of the labour market have been conned into the belief (or manipulated into the position) that staying out of the union is beneficial. In my company, for instance, the pay increases achieved by the union apply to all employees within the scope of the bargaining unit, irrespective of whether they are union members or not. This encourages individuals to freeload, as in the short term, they gain the upside without the monthly dues payment. However, the fewer members the union has, the weaker its bargaining position, as the potential for and effectiveness of industrial action will be less, etc.
