That's true of genuine conversion. (The narrator says--and I think Camus agreed--that conversion is more powerful than destruction.) However, I think here the narrator's fanatical mindset (what you called a "totalitarian mentality," DWill) is so eager to commit to any dogma, without reservation or reflection, that it can't count as true conversion. Tom's examples are apt; it's just easier when you're overwhelmed to box yourself into the given way of thinking. Camus seems to regard this as a weakness of character. I think that explains why the narrator's "maniacal focus" appears to waver at the end: that strength of focus really just hides the abominable weakness of a mind that's ready to cling to anything. That may also explain the last line for me; I can't help but feel that the last line is as objective a voice as Camus is likely to take on in this story, and it is full of contempt for the narrator's ultimately false convictions--like houses built on sand.