> Private sector unions are great for collective bargaining, though I prefer they abstain from broad political platforms (immigration, for example), as these are so far removed the intent of the union. I tend to view these Unions as being political vehicles first, collective bargaining agents second. That isn't a compliment.

The feature you're describing is not an accident. Lobbying for restrictive immigration laws (not just political platforms in general, but that specific platform and issue) is the exact reason that unions like the AFL originally gained the size and political power that they have today.