>So you are equating politeness with not halting bad ideas. That is not politeness, that is incompetence.
In some cultures, direct comment on an idea is the norm, but in others it might be very rude. Even engaging in what you might find to be polite critique can be a challenge; even the most well intentioned comments might not transit cultural boundaries unscathed.
Worse, there might be some context you're missing that causes you to trigger someone without any intent to cause offense.
Example:
A new, senior developer transfers to my team. He puts up a CR and asks me for review. As I comb through it, I find a couple small bugs and take the time to explain why they are bugs, thinking perhaps he did not understand a subtlety in a library we are using. This same library has tripped up a number of developers on occasion, as there is a state that is being manipulated, but under certain circumstances it can be put in a state that is not intended. It's part of a language standard library and not something we can wrap in a safer way, sadly.
He apparently knew about it but just didn't account for it, and he took my explanation to be very patronizing and condescending, given that he already knew the problem. He then read into the rest of the review a hidden malice.
This is partly my fault; perhaps I didn't need to fully explain how the function works, though with the misuse I thought it could be a chance to teach. I probably should have taken more care in some of my verbiage; I tend to be somewhat direct, which comes across stronger than I intend it to. Not "You're a moron, delete this bad code" but more "This function call will not do X, Y, and Z. It will do W instead. Why not use ABC instead?"