We disagree there; to me those two things are part and parcel of one thing.
We absolutely disagree. Those two things are very different.
Zone of Truth is still a thing, is it not?
Failing that, there's real-world options such as references, getting to know the person, etc.
Zone of Truth is trivially easy to compromise with even a modicum of effort. And yeah, do you know how long it would take to RP needing to get references (Which you can't trust) and getting to know them before you hire them (which you can't trust) would take? All of that time and effort in the game devoted to merely reducing the chances of something terrible happening... no one is going to bother with that for more than a single NPC per campaign. It's exhausting.
That's the reality. Which means that's what I'm going to put in my games: that there could always be that one bad apple.
Games are not reality. You are not honorbound to make every PC who wants to have a supporting cast act as a paranoid hiring manager, in real time, at the table, just because people lie in real life. You even said in your aside about your history it was 2 out of 60, that is 3%. That is a margin of error in most statistics, so... why not round it to 0% the majority of the time? Because reality? That's a pretty poor reason to make a game less fun and more hostile.
Same as traps - not every door in a dungeon is trapped but some of them might be.
Ah yes, traps. Classically never a thing that has ever caused any problems, debates, or dozens upon dozens of articles about how they are poorly used, poorly thought out, and are likely harming the game from misuse. As long as it is like traps, then there should never be any discussion about whether or not it is the right thing to do.
Which, also, just wanting to point out. This isn't an "all NPCS" thing. This is literally a sub-set of NPCs. Just like you hopefully don't trap the doors to an inn, why would we need to have our personal maids vetted to make sure they aren't traitors?
Or you just see how it goes. The servant my character has at her house in the game I play in has shown me more loyalty than any other person I've ever met...and taking him on was a pure leap of faith on my part; he's a Goblin (they're monsters, in our games) who was servant to some bad guys we knocked off. We didn't know what to do with him so my character took him in and hired him, not quite knowing what to expect; and it turned out to be one of the best moves that character has ever made.
But it took me a while to realize just how loyal and trustworthy he was. Until then I took precautions, not knowing if he was going to slit my throat while I slept, but soon realized I could relax on that.
Why should every single NPC in your entire house have the potential to slit your throat while you slept? Why can't that just... not be a thing, because it would make for a terrible game experience to actually have that happen?
Oh, and lets say they did slit your character's throat. How long would it be before you decided to take a leap of faith on trusting a goblin again? After all, you were proven that you were wrong to trust them, so why trust them in the future?
50% would be overkill, I agree.
But 5%? That's more like reality, IME.
And at that point, as I said, you can exclude every single Bastion NPC, and still have 5% of all NPCs in the game be potential traitors. You don't need to also include Bastions.