As
@Lanefan said - this wasn't your game.
Oh, ok, if you want to say for this one and only time and reason. As a general way of life, I will never adjust for others.
But my problem here wasn't even about that. It was about a targeted hit job on the PCs with the express purpose of killing the characters for the simple reason that they deviated from the plot you had set out (or whatever the reason was). I honestly don't know ANY players that would like that. Certainly not a casual group at a rec center who are just exploring their interest in D&D.
Targeted hit job? I don't agree that anything not a positive thing the players will like is against the players. Too many DMs see even things like a locked door as something "attacking" the players.
It's not like I cared about the game plot.....it's not my plot. In the first game I just followed the game notes.
Also I don't see "The Multuniversal Hit Squad" to be ANY different a consequence then Bounty Hunters or Guards from the City coming after them. It's Exactly the Same Thing. The alt PCs did not "just" kill the PCs in one second....the players fell for the false story, let their guard down and then acted like idiots when the attacks happened in the game.
I don't play the game you are thinking. If I just wanted to kill the PCs, I'm this type of guy: First minute of the game "All your characters are dead as the whole world explodes. Game cancelled. Bye".
You're "more regular" players know your style and have stuck with it - so sure, maybe they'll have fun. But these were not those players. Again, casual, new to D&D players just looking for a standard experience.
You yourself have stated, multiple times, your style is not for everyone. So you shouldn't spring it on people without warning. Certainly not in someone else's game.
Very few players are just randomly "my type" of player. Nearly all my good players were made by me. It's really part of what I always say: You have to make the players you want. You can't just "hope" random people or your "best friends" are exactly the types of players you want in a game.
For example I want players that role play a character being a follower of a power, not just cheery picking them for abilities and then acting however they want. I do this by house rules, in game, where a clerics power micro manages the clerics spell use. If you follow the powers faith, your power will add boons; if you go agianst your powers faith you can expect your spells to be diminished. If you really go wild, you can expect a more extreme response. It's a great way for players to learn all the ins and outs about their characters chosen power and role play them right.
So, enter my Spelljammer game.....made up of people that are not my type of players. But they agree to follow my house rules as they really want to play Spelljammer. Enter poor Sue who was all upset as she wanted to be a cleric, but hated my houserules. So she does make a lizardperson cleric, of Ka (the dinosaur god of good and life) because he is a multi sphere power(I use the 2E Spelljammer faith rules). She discovers quick that all she has to do is act like a good caring person and Ka had very little problem with her. And more so if she helped others, protected life and nature and did good things....she even got boons and special powers. So she found my "horrible house rule" was not so bad and has tons of fun trying to figure out what her god might want.
And that is just one example, as she is just one of five players. Though they are now five players I would game with in the future, as they are my types of players........now.