Most religious people are quite familiar with the concept of denominationalism.
They understand a denomination to be a part of Christendom at large, and for the most part, they see no essential difference from one denomination to the next. All are equally related, both in their relationships to each other, as well as in their relationship to Deity. To some Christians these questions are perplexing. And you would be right, of course. A more thorough tactic would involve presenting a comprehensive overview of the new testament's teaching concerning the true nature of the church.