The same moral neutrality is applicable to unions.
Afterall, they too are merely a legal grouping of people.
Such a grouping is often necessary to balance negotiation power in the employer/employee relationship.
Abuses can (and do) occur on either side of that relationship, neither is inherently "good" nor "evil".
I agree except that unions exists for the sole reason of creating a monopoly on labor. Corporations exists for the sole reason of increasing profits. A corporation obtaining a monopoly is "usually" short lived because a new innovation changes the dynamics of the market after some time passes. But, there is such upsetting mechanism that exists with Unions. A innovation doesn't do something to knock the unions off of their perch. Also, a monopoly of the type that a corporation can obtain is usually in a market where there are alternative choices (but not always). Unions exists for the sole reason of ensuring that there is no other alternative choice. In other words, unions try to obtain a monopoly on a highly inelastic market, while corporations try to obtain a monopoly on a realitivly elastic market.