And the resultant debate might well be polarising or destructive by itself.
Without knowing what the parent experienced to cause their take on this type of politeness I'm just guessing, though.
It is interesting because I think I see a cultural thing here too: in some cultures "I feel" and "I see" and "currently" are as firm as "unacceptable until it changes" - just worded in a way that conveys respect for the author. But in other cultures it is read as vacillating. Dunno. Guesswork, as I said.
As I said, some people will interpret directness as rudeness. Those are the ones that expect for the language to be couched. But, in my opinion, it's better to be seen as occasionally rude than allow for those other negative behaviors to occur.
What they see is a chance to convince you ("I see...") or refactor ("... in its current form"). What you see is someone who is being stubborn and just not making the changes. So, it leads to a lot of friction and talking past each other.
Of course, it might also depend on that person's reputation and my previous interactions with them. If I have had 50 negative interactions in a row with them, getting such feedback might make me want to throw my laptop into the toilet.
But in most cases I think it would be a good way to phrase feedback.
- Someone injects an obviously inferior idea for political reasons (e.g. the recent TLS 1.3 debate). Then, a rude response might be your best option to deter the opponent. I think, some of Linus's attacks from the past fall in this category.
- Someone is just inexperienced and proposes a bad idea with good intentions. Then go for factual "This is flawed, here is why".
- Someone proposes an idea with flaws, but you see potential beyond the current proposal. Then, one should politely point out the current weaknesses, and at the same time encourage the proposer to improve on it.
As successful leader, you need a repertoire of responses.