The cancer analogy is a pretty good one. It’s not so much that he is actively out to kill himself, as his internal functions are running out of control in a way that is detrimental to his health. In much the same way a malignant tumor in your bone marrow may spread cells into your bloodstream which then spread the cancer to your other internal organs and cause them to cease functioning and kill you, Autocthon is experiencing a sort of degradation called the Elemental Pole of Smoke. This elemental energy is spreading to the rest of his body in fits and starts and is called Blight. In Blight Zones his magical life-sustaining energy becomes twisted and corrupted to damaging energy that corrodes his parts and causes organic growths to form (picture Silent Hill’s Dark World). Living things can not respire Essence in these zones, but dead things and things corrupted by the Blight can.
Now, to understand the next bit, you have to understand that every Primordial (including Autochthon) has multiple souls. These souls are called Devas and are semi-independent entities, they have their own minds and personalities and can even forge new subsouls for themselves. Autochthon calls his most powerful souls the Divine Ministers and each of the Divine Ministers can create subsouls called Subroutines. These Subroutines are part of Autochthon’s soul hierarchy; that is, they are ultimately a part of him in the same way my appendix is a part of me, but are also independent creatures.
Anyway, the Blight can also spread to these Subroutines, which causes them to go insane and destroy everything in sight. This is called Gremlin Syndrome, and the Divine Ministers have created an entire Caste of Alchemical Exalted whose job is basically to hunt down Gremlins and annihilate them while remaining secret to the rest of Autochthonia; that’s how big the problem is. Some Gremlins (particularly those who were infected versions of more powerful or intelligent subroutines) retains enough intelligence to conceal themselves or engage in tactics in their destructive crusade.
The major problem is that Gremlin Syndrome has begun to spread to Alchemical Exalts. This is because Autochthon foolishly linked all the Alchemicals to his brain in order to give them Clarity so they would be less emotionally invested in things and think with Autochthon’s approved brand of pure logic. However, occasionally an Alchemical’s link to the Clarity of Autochthon gets crosswired and instead of being connected to the healthy part of the big guy, they get their brains directly linked to the Blight. This makes them slowly go insane (via accumulation of a trait called Dissonance) which eventually turns them into sadistic monsters who exist only to torture and destroy. The Adamant Caste secret Alchemical cops are trying to kill these people off quietly so that no one knows that Gremlin Syndrome is spreading to the Alchemical Exalted.
The key to all this is that the Blight isn’t destructive of Autochthon in specific. If you took a Gremlin Syndrome-infected Alchemical and put him in a place thousands of miles away from Autochthon, he wouldn’t feel compelled to return to Autochthon and attack him. He would just indulge his unnatural tendency to destroy and torture on whatever was handy at the time. Gremlins and Apostates (i.e., Gremlin Alchemicals) don’t want to kill Autochthon, they want to kill everything. Its just that by default, the only target they have is Autochthon because he locked himself away from any other target.
Note that it is possible for other Exalted to become infected with Gremlin Syndrome as well. Exposure to the Blight may spontaneously cause Voidtech (evil cancerous magitech) to start growing in your body. This grants you awesome robot-cancer superpowers, but drives you insane as above. Thus Autochthon is contagious. Which makes the other Primordials desire to avoid him at all costs much more understandable.