SPOILERS ALERT ABOUT THE END and also AUDIENCES reaction.

SPOILERS -

Why did people have a PERSONAL problem with the SON killing, intentionally or otherwise, the main culprit and yes villain perpetrator of this movie, why were people upset, unhappy, dissatisfied etc with THAT?

Even if Michelle MAY have set it up somehow herself, though even that is debatable, and even if by doing so he (the son) may have put himself at risk or in danger somehow (then again, we see plenty of people doing that in other movies and in other situations, remember how in "Terminator 2: Judgment Day" (1991) John Connor being a young teenager was risking himself throughout nearly the whole film to save his mom from that evil T1000 Terminator? And there are countless other examples too), why was it a huge problem for some audiences?

And also...

Everyone who is civilized and morally outraged often talks about how much they despise the perpetrators of such deeds and even does not mind it when they are killed. But, SPOILERS, how come if that ALSO happens in this movie, even if they don't feel any sympathy WHATSOEVER with the culprit, people STILL complain and get upset and whatnot and accuse the film of being insensitive etc?

But in any case, son killing Patrick the violator of his mother Michelle, why audiences having a problem with that? Why not even see it as a somewhat unpredictable and edgy interesting TWIST in the film? Thanks.