And I said that it's still immutable even in the scenario of all the witness computers getting infected and compromised.
The question was "Can you remove content from the blockchain?"
The only answer there is to that is an unequivocal no, because if you can then it's imperative you show exactly how you can do it, theory or practice.
It's of no consequence whatever hypothetical scenario you want to argue, if you cannot change the data then it's immutable. Obviously we don't live in binary, we live in the real world, and the real world is full of paradoxical things, and something being 0 or 1 is of no consequence to the real world.
In the fully possible scenario I described it is clearly not immutable. Not everything is a paradox and our universe has binaries.