Intensive retreats aren't to be underestimated. It's a serious spiritual path that isn't designed to make one well adjusted to this world right away. I think the end result can be a fully integrated self actualized person, but the traditional view is that it might take lifetimes.
Lifetimes are not what most westerners are (or should be, imho) willing to sacrifice.
Top tier meditation institutions in the west and in Asia are not ignorant of meditation induced psychosis and they have ways of dealing with it. Everyone who claims all meditation is great and nothing bad can happen is ignorant.
Some of my most respected meditation teachers are known for recommending that people don't take up intensive retreats if they feel they have a choice in the matter. If it feel unavoidable, then do it. If it's just something you want to try, don't.
I can immediately recall at least 4 saying this.
However, if 20 minutes of mindfulness a day sets you off into strange psychological territory, then I have a hard time believing that meditation was at fault. The "dosage" simply isn't high enough to be the key factor.