Questioning an individual's approach or statement on an objective topic sounds like an objective topic to me. So what really matters is the heart of your actual question and to ask a question rather than to look for discussion. With sufficient work, to me it sounds like you could ask some of these questions on Stack Overflow proper.
I'll take an example question we had on Gaming. It was retitled to How can the damage reduction from Armor in League of Legends not have diminishing returns?, but its initial title was Why would someone say that adding Armor in League of Legends does not have diminishing returns?. It was asked in response to a comment on another question on our site that the author found puzzling. Which isn't that much unlike what you seem to be trying to do.
To transform it from a subjective discussion to the objective answer seeking which will actually get knowledge rather than back-and-forth, all it takes is a little rewriting to focus the question properly. In the above example, rather than focus on "Why would someone say
X", let's instead assume
X to be questionably "true", and subsequently ask how it is possible for
X to be true. At heart, that is what the author is looking for: the author wants to know the reasoning to which
X can possibly be called true. In the end, we got our answer.
Basically, rephrase your question from questioning people's motives to asking about the core knowledge you seek to learn. For example, the author's choice of a particular algorithm seems weak and you question whether it either was bad design or maybe something is hidden that you aren't seeing: ask about the effectiveness of that algorithm, particularly in the given scenario. You'll either discover that
[this] had significant advantages in the scenario, or that
[the other thing] are superior and the book author sacrificed optimization to instead make a specific point. Or, you might even be told something you didn't even think of yourself.