Absolutely. "Closed shops" are BS. We just took over a facility in a right to work state that was unionized because prior management borrowed money from the union pension fund and had to let the union in as a condition of the loan. One of the first things we did was end the union's ability to automatically deduct union dues from pay checks. Guess what - suddenly not a whole lot of people are interested in paying the dues.
I think unions are important in industries that treat human beings like machine parts, especially where working conditions are dangerous (mining comes to mind) or workers are systemically underpaid (fast food comes to mind). These industries "deserve" to have unions, and the workers need them. Most big American industries have evolved past this, or have outsourced the line jobs that fit this description. In most service industries a team concept has set in and unions are actively deleterious to this concept.
Public employee unions are something of a round peg in a square hole. Some public employee jobs do treat humans like machine parts (sanitation, a lot of low level bureaucrat jobs, to some extent even police and fire and teachers). I support public employee unions to be able to negotiate over work conditions and work rules and protect the safety of their members. Allowing them to create a "closed shop" or negotiate over wages and benefits is a bad idea, because it allows politicians to buy votes on the backs of future generations and it sets the employees interests directly at odds with the interests of the people they are supposed to be serving (the taxpayer).