I, personally, would be very cautious in making a negative blanket statement about the gift of tongues. We, as mere humans, do not have a full understanding of everything, let alone the spiritual realm.
If I classified the gift as pure nonsense, made-up gibberish, what about the True Gift that comes from the Holy Spirit? Would I then be guilty of “Insulting The Spirit of Grace”?
I heard a story: In a worship setting, many were singing in tongues. One woman, who had her eyes closed, was among them. When she opened her eyes, there was someone right in her face, looking intently at her. She asked her if she knew what she was singing, and she said no, she didn’t. The other woman had understood her words and told her she was praising God and was singing about casting beautiful flower petals before the throne of God.
We do not know enough to say that all speaking in tongues is made up, neither should we condemn it, because we lack a full understanding of the Spirit of God and of all his workings. The Bible makes reference to speaking in Angelic Languages. Someone could be speaking in tongues in a heavenly language, and we certainly wouldn’t understand that.