Are labor unions good?

Yes, in general Labor Unions are good, however sometimes they can become excessive in their demands.
Historically Labor unions have been responsible for many good things. The best way to understand the value of Labor unions is to look back in history when there weren't any unions, and compare to the conditions of today.
Books like Upton Sinclair's, The Jungle, show what working conditions were like without unions in 1900.
In retrospect the only people who protest unions are business leaders who want to make maximum profits or people who don't have a union and are jealous.

The question is irrelevant. Only those eligible to join or form a union decide whether the idea is a good one ... then they vote a secret ballot.

It is useless to compare pre-1935 to today and claim that all improvements are attributable to unions, who never represented even half of workers. For example, civil rights laws were enacted over the opposition of unions.

The only people who protest unions are folks outside unions? Bad guess. And even if that's true, such voters are a clear majority - union members are currently a tiny fraction of voters. The fate of US unions will not be decided by a few million union members in a nation of 310 million.