I realize that this might seem like a trivial matter, so I don't blame anyone for having some fun with it, but I think there is a genuinely serious issue here.
When you use profanity, there is usually a purpose to it: It helps to convey something beyond your other words. For example, it might be to emphasize how strongly you feel about something, or to convey an emotion such as anger or contempt, or for a certain kind of humorous effect. In face-to-face communication, you can express these kinds of things using tone of voice, facial expressions, gestures, and so on, but in writing you don't have those options, other than perhaps putting a word in a different font or adding an appropriate emoticon: The effectiveness of your communication depends entirely on the specific words you you use. When you say that an amp sounds like s**** or that someone is full of s****, it really matters that you used the word s**** rather than something else, in terms of accurately conveying the message you intend.
Conversely, when an adult uses the word "poopie" in a conversation with another adult, this suggests that the message one intends to convey is very different: You'd only use that word if you were trying to convey a very different kind of message: e.g., you're trying to be "cutsie" (expressing a particular kind of humor), and/or you are deliberately to make clear that you are not being serious (or not feeling genuinely angry, etc.). So, changing the word "s***" to "poopie" can fundamentally change the meaning of a communication, as interpreted by those who read it. And that's why OP is so (justifiably) upset. If his profanity had been replaced by a string of asterisks, everyone would be able to accurately infer that he had used a "bad word" -- even if they couldn't be sure which particular word he had used -- and that he hadn't written "poopie" deliberately; they would therefore interpret his message very differently.
So, although the automated s***-to-poopie conversion is a cute idea, I think it is entirely inappropriate because it has very real effects on the way a person's posted message is interpreted. I usually find myself siding with the admins on issues like this, but this time I'm firmly in OP's court.