Just a fetish or something deeper?

So I was watching a show on youtube earlier, it turns out it was about fetishes. It was a actual movie, it looked interesting so I started watching it, but had no idea it was about fetishes until it got a little further into it. There was a man who loved to be in diapers, and wanted a strange woman to treat him like his mommy. He sucked his thumb etc. It had me wondering, if fetishes are just that, fetishes nothing more nothing less, just a fantasy type of thing. Or is there something deeper behind the fetish? Thoughts?

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