They don't go off to college and lose it.However, a lot of perfectly healthy, well-adjusted 20 year-olds go off to college and lose it. Point being, the parents are not to be judged guilty sans any knowledge what so ever.
With respect, you are confusing mental illness with brain-washing and indoctrination. Do you know what a "Liberal Arts" program in college actually means? It's when colleges take young, impressionable, well-adjusted individuals and literally do their best to brain-wash them into becoming extremist, hate-filled Liberals. I know, because that's what John Jay College tried to do with me in the mid. 1990s. Failed miserably to do so because at the time I had no clue that I'm an INFJ personality type. Only 1%, possibly 2% of my kind out in the world. Translation = I literally think differently than 98% or 99% of the rest of the world. So the standard-issue brain-washing program didn't work on me.
Though I'm sure my parents enjoyed paying for the privilege of having their optimistic and well-adjusted son be put into an (ironically) non-Government sponsored "Re-education" camp disguised as an institute for higher learning. Lenin and Marx would have been impressed.
Mental illness can develop later in life. Though we're then talking about a severe physical or psychological trauma that can be traced. Most mental illness, children are born with; and their parents see it. So again, not guessing. A realistic outlook on mental instability.