Every generation has some product/ingredient that they didn’t know was dangerous at the time: tobacco, lead, asbestos, etc. What is that item for this generation?
Wait... vegetable oil? Like, olive, canola, avocado, coconut? I have never heard of this.
Edit: Commenter below helped me understand you're probably talking about hydrogenated oils. Seems misleading to say vegetable oil is a silent killer. You're not wrong about heavily processed foods, though. (Thanks @mindrover@lemm.ee !)
I think the raw oils are not that bad (maybe in quantity it becomes an issue). Coconut oil I know is saturated fat, so that can be bad for your heart.
I think the bigger issue is how they are used in processed food. Just about every processed food has "partially hydrogenated soybean oil" or something like that, which is basically the worst possible thing for cholesterol.
It's the same with how everyone started using Crisco because lard was thought to be unhealthy. It turns out heavily processed vegetable oils are worse.