Unions

I was listening to NPR the other morning and they were interviewing someone who was part of a group that recently broke with the AFL-CIO.

This woman said that the group she represented was going to stop trying to recruit employees of a single business and instead widen their search to entire communities. For example, she said they would try to unite all the child care workers or all the janitors, in a whole community.

What I am wondering is if the good effects of a union outweigh the bad effects on the economy? It seems to me that a group of people who are controlling the price of their services in a community would set those prices higher than consumers would be willing to pay for them if there was competition in that sector.

Hypothetically,
Would the point of a Union of Childcare workers in Cache Valley be to protect those child care workers from (exploitation- or i don't know what) or to reduce competition and use the union as a way to raise their prices and make more money?