The employees are entitled to hear both sides and make their decision. They do have the right to unionize. And a vote on whether or not to unionize seems like democracy in action. The way to keep unions out of a facility or shop is to treat their employees fairly, listen to them and educate them on the benefits of not unionizing- not to hold their hand and teach them to "just say no"- as though the correct answer is always "no." If upon hire, employers don't trust their new employees to think for themselves, what are they ultimately saying about the people they just hired?
Unions protect the employee in the era of "employment at will," in which one can be fired for any reason whatsoever, fair or unfair, and without recourse (except obviously for protected classes that may be able to prove discrimination based upon age, race, etc.). Thus, harshly realized, companies are free and able to ruin your life at any time, for any reason. It is often misunderstood that employees have rights. Further, employees have many misconceptions as to what the labor laws actually say. Without a contract (or implied contract), employees are only entitled to unemployment benefits if they are terminated without just cause.
Union representatives do sometimes make promises that they can't keep because until a union is put into place, it has no ability to bargain. As an employee, the decision to consider a union, or to instigate one, is risky. Rumors spread fast, and even though one can't be legally fired for talking about unionizing, employees are vulnerable since companies don't always behave- especially when their profits might be at risk.
The case against a union stems from the fact that unions often protect only the "poorly performing" employees. They create a lengthy and time-consuming process toward termination- resources that could be offered to good employees in the form of wage increases or benefits. Employees often take advantage of the situation, aware of their protection, and the rules, to perform just well enough to prevent being fired. Besides being expensive and time consuming, it can also create an uncomfortable workplace environment- that is, an "us against them attitude."
Unions are entitled to review employer financials to negotiate fair wages. In a country in which the richest 10 percent own approximately 70 percent of the wealth, it is clear that profits are not trickling down to the employees. And unionized employees do, on the average, make more than non-unionized employees. At the same time, this often ties management's hand to reward their better employees, since increases are often predetermined. And since benefits and wage increases are often agreed upon in advance, the incentive for employees to go "above the call of duty" is often removed. Thus contrary to intended purposes, unions often protect the poor employees while holding back the good ones. Hence, good employees working for good companies should not want union, while poor employees working for bad companies should insist on one.
Ultimately unions establish a contract that binds employees and employers. Their terms are agreed upon and contracted so that the conditions are apparently clear and fair. There are many advantages and disadvantages of being unionized, and ultimately that decision should be left to the employees. The employer should stress the advantages of not being unionized and prove that fair treatment is possible without a union. However, I believe that it is demeaning and belittling to go so far as to reenact scenes instructing the employees on how to act if approached by a union. Fair treatment of employees should be the deterrence that keeps a union out, not propaganda and negative campaigning on how to "just say no."