In regards to invitational rhetoric, if we believe it to be a form of persuasion, I feel that there is a flaw in its structure. When persuading someone we are trying to convince them of a specific idea, concept, believe, etc. So, it is important for the persuader and the general discussion to stay on topic and not have outside forces drive the conversation away from designated topic.
However, with invitational rhetoric we develop a discussion with the person we are trying to persuade which can often get off topic and away from the point. When you invite people to think about and question the designated topic it can lead to other questions which may separated from the original topic. This is not to the benefit of the persuader as his point can often become buried by other topics. So, when talking about rhetoric and persuasion, In my mind invitational rhetoric is not a very effective form of persuasion.
That being said, if your objective is to discuss ideas, expand concepts, and question general knowledge then invitational rhetoric is a very effective tool. However, when trying to persuade someone, the conversation tends to get muddied when you bring in others opinions and thoughts on other topics that get away from the original point trying to be made.
I guess my post also raises the question of how moral rhetoric is if you have to force someone to forgo there own opinions and thoughts.