We know from casual observation that if anybody does respond to their preaching/recruiting work it is usually someone that is a social misfit in some way or a person that was indoctrinated early in life.
Think about all the nicer neighborhoods witnesses preach in. If a family of four with a father that is an engineer and a mother who is a medical professional ever walked into a kingdom hall for the first time and said they were studying, people would faint. Lol...
This of course isn't what you would expect from a religion backed by the ultimate intelligent creator. If they actually had the truth, the smartest people in the world would flock to them.
In all seriousness, though, have you ever seen an educated middle or upper middle class person or family join this religion? If so, how long ago was that?