I have absolutely no problem with you not liking this particular type of scene in an adventure (published or no). But to say that it's 1) bad design to include this scene (which isn't objectively true and only your opinion)... and 2) to attribute vindictive motives on the part of the writers for including it and for DMs for running it... that's just a bit much.
First of all, it is my subjective opinion that putting in massively powerful foes that are basically there to be only interacted with in one and only one way is bad game design. Yes, that is my opinion.
I don't see the need and I do see the harm. I don't see the need for the DM who accidently killed his PCs with the blue dragon because he didn't carefully read that the dragon did so many dice of damage with its breath weapon.
This is not just about the design of the module, it's about the propensity of bad module design to kill off PCs when that is not the intent of the designer. The first encounter in Lost Mines of Phandelver had NPCs who could attack, move, and hide all in a single round. And because of this, there were TPKs or partial TPKs in that first encounter. There was even a thread here on EnWorld where a group decided to never play 5E again because of it.
There were TPKs with the green dragon in LMoP because the PCs were encouraged to fight the green dragon and even one of the PCs had a background to strongly encourage it.
The harm is that PCs die and players might get annoyed enough to not even play the game anymore. Is that what we want with 5E?
So yes, it is my opinion that impossible or nearly impossible foes is terrible game design. Tough foes, but not unbeatable ones (or at least unbeatable without certain fairly common specific classes/spells/abilities and DM fiat to override certain encounter silliness).
And now that I know more about this particular encounter:
a) shame one PC into fighting or
b) shame most of the good aligned PCs because an NPC goes to his death or
c) TPK or partially TPK the party because the players refuse to be browbeaten in this way or
d) possibly have a group of PCs with just the right types of abilities along with a DM who is willing to blow off aspects of this nonsensical encounter and the PCs might eek out a win (where this last option is probably rare at most tables).
Sorry, but this set of choices is terrible encounter design. It's not about morality of PCs, it's about browbeating the PCs via morality and if that sounds like I am attributing vindictive motives on the designers, so be it. They might not have intentionally decided to create a rat bastard encounter, but that's what they ended up with.
Did they not playtest this? Did not a single player complain? Did not a single group of PCs go out and get TPKed?
At our table, the DM originally described that a dragon was flying above the town and the town was on fire and there was a serious discussion before we even got there as to whether us first level PCs should even go there. We were trying to roleplay our PCs, but had a difficult time justifying going anywhere near the town.
This is NOT good adventure design. The only reason our PCs went to the town at all was because of the metagame knowledge that this was a module designed for low level PCs. The very CONCEPT of low level PCs heading to a town that is under attack with a dragon flying overhead is totally ludicrous.
Talk about out of character. If we were really living beings in that situation, many of us would walk in the opposite direction as fast as our legs could take us.
Duh!
Just because someone writes something down in an adventuring product does not make it a good idea. This entire set of town scenarios was ludicrous from the very start for low level PCs.
You can disagree and that would be your subjective opinion.
Btw, I was also not impressed with the number of encounters that we had without a long rest. These are first level PCs. The only reason our group did so well is because LMoP taught our players how important the group stealth skill and a surprise round is. This is what my group learned about 5E with LMoP. Even our fighter who is disadvantaged with stealth trained the stealth skill so that he would not always miss a stealth roll.