There's a lot of information, contrary and positive to the use of dummies.
They can be of enormous benefit for premmies, fills that need for suckling. But it's when it becomes a habit, or the only means of self soothing for a child, or interrupts normal development, that they become an issue.
Watching Harry. He talks with it in, ideally he should be told to remove it to help with word enunciation.
They can play a role in ear infections, and tooth misalignment, and over bite issues with dental and mouth development. Not all may be affected, but there can be long term issues for others.
It's all about being aware of their use and making informed decisions, and when appropriate weaning them off their use.