"When GM offered the UAW more lavish benefits, it did so in order to induce the UAW to accept less generous wages. The money that GM paid in the 1990s and 2000s to fund pension and retiree health bnefits was offset by wages that GM did not have to pay in the 1960s, 1970s, and 1980s. Lowenstein appears to want to live in a world in which GM (a) gets a break on its wage costs in the 1960s, 1970s, and 1980s; and can do so (b) without having to pay any money to fund pensions in the 1990s and 2000s."
Bad management screwed GM, not not the Unions. GM ought to have set aside the money saved on wages to meet these future obligations. That they did not do so is just one of many examples of their management incompetence.