I disagree. They are hard on brains of some humans, mainly due to motion sickness. But that happens only when there is artificial movement involved - when user's movement doesn't match camera movement.
And it really depends on the person, some are more susceptible to that, some are less. I also think some resilience to that effect can be trained with practice.
Then there's the style of artificial movement provided by software. I've seen several solutions which make it more bearable - generally those involve some degree of physical activity beyond just pressing a button.
Adjustment of focal plane seems like a rare problem; it's honestly the first time I hear it mentioned as an issue which is "very hard on the human brain". Usually it's all about motion sickness.
> but I have yet to see any usage that would justify spending spending as much one one as I did my TV
For me, it's about activity it provides as much as it is about immersion. I wanted to reduce my time sitting idly, and VR lets me do just that without abandoning gaming at all.