The other side of the coin is why should people who don't want to collectively bargain have a veto over the people who do? (Since that's what happens when management can circumvent the union -- the union loses its bargaining power.)
It is unreasonable to equate imposing something upon others and "imposing" nothing upon others. When all else is equal, the higher bar ought to be placed upon the imposition of additional layers of bureaucracy in other people's lives.
As for how to choose, I'm not sure.