There seems to be a contradiction in something that is immutable and yet can still have content removed.
Its a paradoxical statement this:
The blockchain is immutable, but like any council, the witnesses can still remove content like CP if it does appears on Steemit.
It being contradictory has no value because it's still true, therefore it's not merrily contradictory but paradoxical.
How do you consider it to be true?
Can the blockchain be changed or not? This isn't some sort of quantum super state.
"Can you remove content from the blockchain?"
Without complete knowledge of the inner workings I will hazard saying yes from what I understand. I believe that a consensus of the top 20 witnesses could push through an altered blockchain but I could be wrong.
Let's assume they can for argument's sake. That would mean that the blockchain isn't immutable since it can be changed in that scenario. This relies on the blockchain being defined as the current live consensus version.
You've added a restriction that it must be changeable by an individual. No such restriction should be expected when calling something immutable. Immutable as a term on it's own in binary, it is changeable or not. I also specifically stated that it relies on the definition of the blockchain being the currently accepted consensus. That does not include backups and rogue chains.
In the fully possible scenario I described it is clearly not immutable. Not everything is a paradox and our universe has binaries.
The probability of it happening has no bearing on whether it is immutable. The ability to change it is baked into it's design. Just like ethereum is not immutable they changed the blockchain.