I’m not sure if you’re referring to Buddhism when you say you have “a problem with the forms of spirituality or religions that uphold the principle that existance is a illusion”. But, having run across the misconception that Buddhism actually holds this view quite a bit recently, I’d like to address it.
I completely agree that this idea would be problematic, but I don’t think that it is an accurate representation of what Buddhist thought actually is proposing. It is a cursory reacton to a surface-level and simplistic reading (or, perhaps, rumor) of what Shakyamuni Buddha was actually noticing about the nature of the fabric of reality.
Buddhism does NOT hold that all is illusion at all:
“With all this talk of . . . the illusory nature of phenomenon we might conclude that ourselves, others, the world, and enlightenment are totally nonexistent. Such a conclusion is nihilistic and too extreme. Phenomenon do exist. It is their apparently concrete and indipendent manner of existence that is mistaken and must be rejected” (Intro to Tantra, Lama Yeshe).
The Buddha did not point out that all phenomenon were empty of existence, rather, he pointed out that they are empty of any inherent SELF-existence.
I believe this misconception that Buddhism holds all to be illusion stems quite naturally from the Buddhist notion that everything is inherently empty. However, emptiness and illusion are very different things.
Illusions, projections, delusions, cravings, aversions, concepts, and self-grasping all stem from the ego’s frantic need to find some kind of stability amidst the deeper intuitive knowledge it has that EVERYTHING is inherently connected to everything else in a huge web, the basis of which is emptiness, and therefore nothing has any inherent self-existence. The basis of ego is the frantic denial of this underlying interconnectedness. Buddhism is the path of understanding how ego coopts mind to distort the fundamental interconnectedness of all reality.
“Even though it is sometimes said that something is non-sexistent because it is like an illusion, a dream, or a reflection in a mirror, this is not philosophically correct. It is speaking loosely to say, ‘This phenomenon does not exist because it is an illusion. It is just one of my projections.’ In fact, the reverse is true. The phenomenon exists precicely because it exists as an illusion, which is inter-dependent. A reflection in a mirror is also interdependent; it exists because of the mirror.”
In other words, all phenomenon that arise, arise dependently from the field from which they arise, they don’t exist in and of themselves. So, the only illusion is that things actually exist as their own entities in the sense of being their own, self-originated energy.
We usually equate existence with indipendence - something exists only insofar as it is distinguishable from other things. This is true on a relative, gross-level plane.
To say that something exists simply means that it functions on a relative level. But when we look at the deepest components of the fabric of reality, down to the quantum level, there is no actual demarcation between any thing and anything else. All IS one. But nonduality does not mean nonexistence.
The tension between the relative and the absolute is the mysterious, creative field from which all phenomenon arise.