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We can get all technical but that's not the point. The point is WHY NOT? Personally feel like it limits the audience and topics people are willing to talk about. If you can delete people will be more open and honest bottom line, not the opposite.

like he said before. because the data goes into blocks on a blockchain, which is essentially a distributed database that only moves forward changing states as needed linearly into the future. in short, you can NEVER delete something once it has been officially added to the blockchain, unless you restart the blockchain from scratch.