Honestly, I think this is the wrong question to ask.
If the goal of an introductory class is to teach basic computer science, algorithms, programmatically solving problems, then your course is fundamental and you can choose one based on clarity, simplicity, and getting your ideas across. Some functional languages will be great for this. Particularly if the students have little or no previous experience.
Usually this isn't really the goal of many introductory classes, though. They may require certain techniques or certain languages for a later course. They may want to leverage particular libraries, etc. They may just have to match someone elses checkbox list of "features".
So I think you want to turn your question on its head. Figure out what it is the course is actually trying to achieve, and pick the best language you can for that purpose. In some cases, this may be a functional language.
If what you are really asking is how best to teach introductory level programming and computer science, that's a different can of worms.
