Because they're unfair to the majority who cannot be unionized, and unfair to those who are forced to join and forced to strike against their will.
When I see crap like this happening, particularly in what some call the Second Great Depression, I'm inclined to risk the fury of unionists to say, "ENOUGH! NO MORE UNIONS!"
Besides, they may well have destroyed the North American automotive industry. Yes, the finger of blame must be pointed at unions FIRST. Followed by the eunuchs in the biggest offices of the auto industry who caved in each and every time just to keep things going, to hell with the ultimate consequences, which have, yessir, happened, despite the denials that they ever possibly could. And the politicians, particularly the Leftist ones, who claimed that unions were a "right" (they aren't, as they infringe on the rights of those who aren't unionized, thus negating the "association" rights of unionists because they infringe on the equality rights of those who aren't unionized, so the Supreme Court must strike down pro-union laws as unconstitutional). After all, like the Left says, "You can enjoy your rights as long as they don't infringe on the rights of others".
Ok, who's pissed off at me now? Keep in mind that I don't belong to a union and make only 1/3 to 1/2 what you make (before benefits, of which I get none) and work in a crappy place with bosses who usually think about themselves first, so think about that before you badmouth me, you lucky-wuckies.