Oh, I'm sure that there are such folks, but if I'm asked what I think of it, I can't see any logic in that position or, for that matter, any Biblical reason to adopt it.
Again, if you ask me, I can't agree. I can appreciate why they say what they do, and I CAN accept the general principle, but I can't see that reciting a prepared prayer is automatically insincere. If I read a prayer and put nothing of myself into what it states, then that would be wrong, obviously. If the sentiments expressed are clearly slanted by the author to bring about a phony agreement with some political premise, for instance, that's wrong.
However, almost every prayer that I recite from the prayerbook used in my church reflects my heartfelt and Scripturally-correct sentiments, so to say that there's something wrong--or that I cannot emotionally connect with what I'm saying when reading it--is just arbitrary. And frankly, I think there's a good argument for the OPPOSITE view.
Personally, I grow cold at hearing nothing but awkward, inarticulate, repetitious extemporaneous prayers offered by people on such occasions as grace before meals or at a Bible study group, for instance. They're sincere and I appreciate that, but they don't relate to me very well
By contrast, some of the prayers that I find in a book can be tremendously uplifting and beautiful. And there's no reason to say that the words are not sincerely meant by me when I recite them, not any more than the hymn "Amazing Grace" or the 23rd Psalm--both of which owe to someone else's pen.