....”This is a cornerstone concept”...
Could you enlarge on this meaning?
The most important thing to do when faced with a "deprogramming" problem is demonstrate that the new age teachings cannot be substantiated through mathematics or physical experiments. The new age seers are generally not particularly well-versed in actual sciences. It is an easy task to demonstrate this. From that point it is easier to discredit those teachers: If they don't know or understand classical physics, how could they know and understand super-duper-interstellar physics?
Each individual must judge for themselves if they are being snookered. The rest of us need to equip endangered individuals with the tools of discernment.
When you boil it down, new age followers are rather ignorant, but rarely stupid. Stupidity is permanent while ignorance can be cured through education.