The real reason Klaus should have felt regret:

[doetwin]

After Stephano's arrival in TRR, DH stated that Klaus would, years later, regret not yelling to the cab driver to take Count Olaf away. I always thought it was rather odd how Klaus thought that this would have worked, or why it was any more on him than Violet. First of all, what were the chance's that the cab driver would have even believed him? Secondly, even if the cab driver had believed him, how was he going to get Stephano back inside his cab and drive him away successfully? Simply put, Klaus regretted his neglect to carry out a plan that was highly unlikely to succeed.

However, Klaus still had a legit to reason to feel somewhat responsible for his uncle's death. Even though Monty was wrong about Stephano's identity and intentions, he put a dent in any sinister plan of Stephano's by tearing up his ticket for Peru. He planned not to let Stephano know that he wasn't coming along until the morning of, by which point, it would have been too late for Stephano to form a plan. However, when Stephano confronted about the fallen lamp, Klaus just had to blab Monty's plan to Stephano, giving him an entire day to formulate a brilliant plan, which he did.

Ironically, though, it never seemed to occur to Klaus that had he not opened his mouth, his uncle may very well not have died. You would have thought that he'd learned his after announcing to Count Olaf that he'd figured out his "marvelous marriage" plan in TBB as soon he figured it out, an action that almost cost Sunny her life.

[Dante]

One of the things I like about the earlier books is that the Baudelaires have slightly more individual characterisation. Klaus is frequently rash and prone to anger; emotional, tending to speak and act without thinking. The children start to blur together a bit in the later books, the same character with three separate talents, and the individuality is lost, which I think is a shame. Anyway, while it's true that Klaus's regret is somewhat irrational, I imagine people regret things which were not strictly speaking in their power all the time, but you're right that a separate event seems like it should have been a greater cause for regret.

[vfds321s]

Klaus wouldn't have made a difference then either. It's obvious that Stephano already knew that Uncle Monty was going to tear it up, as seen when he pushes the lamp over to injure Monty's shoulder. Plus, I'm very certain that he was going to murder him from the start, regardless of what the Baudelaires and Dr. Montgomery did.  

[Foxy]

Feb 11, 2019 18:00:10 GMT -5 vfds321s said:

It's obvious that Stephano already knew that Uncle Monty was going to tear it up, as seen when he pushes the lamp over to injure Monty's shoulder. 

I suppose it is plausible Stephano could have heard the children's and Uncle Monty's outdoor conversation from Klaus's room. It is kind of scary to think of Stephano sneaking around the bedrooms in the upstairs of the house while everyone else was outside. But I agree with doetwin, and I don't think Stephano knew what was going on. I think he is just a terrible, murderous person. 

Dante, I never realized what you said about the kids more or less being the same person as the series went on. I see what you mean, and that is disappointing. It's kind of like they all become volunteers, and volunteers are pretty much all the same person. I do agree Klaus was more prone to anger in the earlier books. He was an angsty preteen. Sometimes I actually do think the kids were maybe a bit spoiled, but not enough to warrant Count Olaf’s behavior toward them. 

[Uncle Algernon]

Feb 11, 2019 18:00:10 GMT -5 vfds321s said:

Plus, I'm very certain that he was going to murder him from the start, regardless of what the Baudelaires and Dr. Montgomery did.  

Hm. I forget the details, but I believe the Snicket Sleuth disagrees there…