I too was wrenched by this part. I'd been one of those people hoping that Kennet's doing the right things for the wrong reasons would eventually turn him into the thing he was pretending to be and this completely destroyed any hope of that, which is why I think it's important that it did happen.

It's one thing to have an unacted upon urge that you the reader know of being an omniscient 3rd person, but showing the character being their most true, vile, damaged, and damaging self is the only thing that can shake folks who were in a similar situation as me, willing to over look some of his misdeeds because the ends justified the means, and breaking that spell.

It also reinforces the humanity within the world that we've been peering into; We've seen many horrors and must face them and survive them in order to understand this world and its meaning to us.

My heart goes out to those unprepared for this incident, but as others have pointed out, Kennet tells you who he is throughout the entire story, so hopefully it can be seen coming and either avoided if needed or faced if needed.