Wasn't the plan of vaults to test the human population in an enclosed space so that they knew what they were in for when they decided to travel on a spaceship to a new planet which wasn't all fucked up? Like, if we're going to do a spaceship journey to another solar system then what if X happens, what would that be like and what can we do to prevent it?
I mean, the vaults have to have some kind of a point to them. They're not "just" about saving people, so what else is the point to them? The spaceship thing is kinda silly to me but at least it offers a believable reason for some of the more inhumane experiments. So an FEV vault? What's the point of that? Like, really, what is the point of a vault dedicated to experimenting on FEV? So that they can what? Make super humans in space? For what possible reason? The vault with the sound thingie that made people cray cray makes sense as it could happen on the spaceship that the audio system fucked up and some kind of noise could make people go mental. But FEV? Cloning experiments? Molerat experiments? What's the point of any of them? What would those experiments really bring to the table?
And if we're not going with the space adventure reason for vaults having zany experiments in them then what's the reason? No reason? Oh that's right, I forgot, it's Bethesda we're talking about here, they don't give a fuck about a reason.
And hell, even the vaults that had experiments in them didn't plan to kill the population a lot of the time. Vault 15 was to test how people from different cultures would cope in that kind of environment. That the vault fell apart and the people left it was because of their own fuck ups, not Vault Tec. Same with the gambling vault. Same with the weapon vault. Same with the political sacrifice vault. The experiements weren't to outright kill the inhabitants but to simply monitor un-ordinary situations and how they coped with it. Any vault that collapsed did so because of the inhabitants themselves most of the time. Other times they just up and left, and some vaults were never meant to fail in the first place.
But vaults by Bethesda just seem cartoon villain-esque. I mean, everyone who participated on the construction, design and plans for the vault were all inhuman pieces of shit that were like "ey yeah dis gon kill peeps ya? whatevs, still got ma cashmoney!"