"I haven't a clue exactly how anarchy (a state of being without a clue to progress is one definition of anarchy) is exactly desirable as an end goal."
That's because you refuse to define anarchy correctly.
"It depends what your notions of "normal" and "boundaries" are, I guess."
No, it depends what your notions of "right" and "wrong" are.
"If by "opposing slavery" you mean breaking into slave markets and causing a bit of "heroic idiocy" mayhem and violence..."
Opposing slavery means breaking into slave markets, freeing the slaves, and preventing the slavers to profit from slavery in the future.
"I would say that would be a better, more useful thing than getting burned at a stake or dying on a cross."
Of course. But freeing the slaves also means: If they don't know that they are slaves, or refuse to accept that reality because it makes them feel uncomfortable, anarchists can experience violent backlash even from the slaves. In most cases it's not the authority that burns or crucifies the anarchists, but the obedient slaves who follow orders out of fear and mind control.
"Call me awkward, I don't really understand this obsession with suffering for a cause to the point of extinction."
As eternal beings, there is no extinction. But being forced to live on a prison planet, deprived of memories and spiritual evolution, slowly fading into oblivion, is the bigger suffering. If you're okay with that, you're like that corrupt guy in the Matrix movies who wanted to be brought back into the Matrix and forget the real world.