I've previously said I don't like Passive Insight, it doesn't make sense to me - I'm strongly of the view that NPCs can't force PCs to believe them through a Bluff check, which IMO is the only situation where it would make sense to have NPCs rolling Bluff vs PC Passive Insight - that's how it works when PCs try to bluff NPCs.
I was listening to a bit of the Chris Perkins/Robot Chicken game on youtube and I noticed that Perkins doesn't use it either. He was playing the quest-giver NPC, the players were sceptical of her motivations.
Perkins:
"If you doubt her, you can make an Insight check to see if you think she's telling the truth."
*roll roll*
"With a 16, you're pretty sure she's not lying to you."
I think this is a good approach. It's close to how I've done it, and a good reminder to the DM to remind players that they can choose to use skills like Insight which often get overlooked.
I'm not sure that approach actually implies the lack of Passive Insight.
My approach has always been that I might roll against Passive Insight if a PC is being lied to and the
player is not suspicious. Basically, a high enough insight means the player gets a 'heads-up' when something is off about what they are being told.
If the PC, however, is suspicious in their own right, they can certainly attempt an Insight check to try and get a sense for whether they are dealing with deecption or not.
And, regardless of their result, the player can always come to their own conclusions. Even if everything they are told
sounds smooth and reasonable, if they really are convinced they are being told a lie, they can certain react accordingly.
How precisely do you want to handle things in the absence of Passive Insight? I can only see two real approaches, and neither one is especially good:
1) Whenever an NPC lies to the PCs, you don't roll Bluff. Unless the PCs actively state they are suspicious and ask to roll Insight, the NPC does not need to roll anything in order to lie, and even the most insightful PCs don't have any way to note inconsistencies.
I suppose this can work in a campaign heavily driven by player skill, and which PC skills are intentionally marginalized. A really good DM will be able to pepper falsehoods with clues and inconsistencies that the PCs can pick up on, at which point they might ask to roll Insight to figure out what is going on.
Or, as I suspect is more likely to be the case, once PCs realize that Passive Insight is out the picture, they turn to the need to analyze everything, and will request to roll Insight checks against everything they are told, just in case. Which tends to slow things down to a crawl, while offering no real benefit.
2) Whenever an NPC lies to PCs, you roll Bluff, and ask them to roll Insight. And when they all fail their rolls, you kindly ask them to just ignore the fact that they rolled that, and hope that even though the PCs are clueless, the players now totally know that something is going on.
A DM might be able to remove that by throwing lots of 'false' insight checks at the group, just to keep them on their feet, and so they never know which ones are real. But clever PCs can still often figure out from context, and either way - again, you end up slowing things down for no real benefit.
Conclusion: I like Passive Insight. I just think you need to use it properly, and from your post, the problem may have been that you aren't doing so. As noted above, the excerpt from Chris Perkin's game does not in any way go against Passive Insight - the second that players become skeptical and indicate they have doubts, the 'passive' part has
already gone out the window.
It is exactly the same as Perception. If PCs are traveling down a road, and someone is hiding in the bushes watching them, I'll roll against their Passive Perception to see if they notice. Or if they are walking past a clearing with valuable herbs in it, I'll check their Passive Perception to see if they notice.
But if the scout says, "Hey, I'm looking around for anyone planning to ambush us", or "Hey, I take a closer look at that nearby clearing", then we are into active checks, and the scout actively rolls Perception.
Same exact thing. If an NPC lies to PCs, I roll Bluff against Passive Insight. If they see a group of people who are acting strangely, I'll check their Passive Insight to see if they notice. Whereas if they actively express suspicion about her or are actively curious about the unusual behavior, they go ahead and roll their checks directly.