You are the only one who knows what "condition" your body is in. A year ago, I would have reacted the same way as your friend, if someone I cared about told me they were doing this. It is all a matter of what we have had ingrained into us all of our lives, and what amount of education we have acquired regarding nutrition ... which by the way is SO contradictory to what we have grown up to believe.
I am not a nutritionist, but I do read alot about this so that I can gain knowledge. "Happy is the man who haveth wisdom and who getteth understanding". It is not enough to just do this and not understand why. Some of the people who care about you are not ready to receive the information, therefore they are against it. The more you educate yourself, the more you will feel confident that you are not doing anything harmful, AND you can begin to educate your friend and other loved ones by sharing the information you have learned.
If you feel that you can go on to day 14, I say go for it, but I am not a doctor or a nutritionist. Always keep in mind that not many on this forum are, although there appear to be SOME. It is a great place for support and to learn from others' experiences. I learned of this cleanse through my health and nutrition class at church. But I then did my own research. Just my suggestion.