The reason I'll never watch this (spoilers)

I suppose it's no secret that this is the one where Poirot dies. I suppose the events leading up to his death are also no secret:

-Poirot knows the real identity of the killer, but there is no evidence that would convict him.
-Poirot therefore takes the law into his own hands and kills the murderer, to prevent further murders
-Poirot's sense of justice dictates that life must pay for life, and so he takes his own life

Now, the reason I'll never watch this isn't because Poirot dies. It's because of the convoluted plot. First of all, Poirot is Catholic, and suicide is an unforgivable sin to Catholics. Worse, even, than cold-blooded murder (because after murder, one can at least repent). Second of all, why not turn himself in? He kills himself because he took the law into his own hands by doing something illegal. Well, in killing himself he again takes the law into his own hands by doing something illegal (suicide was illegal in Britain until 1961).

Thirdly, what about the whole Murder on the Orient Express affair, where he allowed quite literally a train-load of murderers go free, because he felt that they didn't deserve punishment? The logical inconsistency of the first two is bad enough, but with all three points here, it borders on the preposterous. Poirot was a stickler for law and order, meaning even if he compromised his principles by committing murder, he would then logically satisfy his sense of justice by letting the justice system decide his fate.

I don't mind a celebrated fictional character finally meeting his demise, but by all accounts the plot here is just silly. And that I do mind.