adverbs - Explaining "despite" as a preposition

My question is provoked by a desire to better explain to my students grammatical conventions regarding "despite." I am finding that my own explanatory resources come up short in this regard.

Erroneous sentence:

Despite there are many critics of Halloween, it is important to
take a look at its positive aspects.

I understand that "despite" is a preposition. A preposition must take a noun phrase or a gerund as its object. Thus the sentence can be corrected this way:

Despite (the many critics of Halloween / the constant criticism of
Halloween) , it is important to take a look at its positive aspects.

What I think is happening in my students' erroneous sentences is that they assume the usage of "despite" will conform to sentence structures that employ adverbs of contrast. My students grasp that the function of despite is to set up a contrast, but then assume that they can employ it as they can "although" or "while" :

Although/while there are many critics of Halloween, it is important to take a look at its positive aspects.

Here's where I begin to become entangled myself. I want to be able to demonstrate to them that "although" and "despite" differ in that the first is an adverb which can modify a whole clause, but despite can only modify a noun phrase. However, if I want to show them analogies with basic prepositions I run into difficulties.

What I want to show to my students as an analogy:

"In / Slovakia's eastern region, / it is important to learn Slovak."

Preposition / noun phrase, / sentence

"Despite / its many critics, / it is important to look at the positive
side of Halloween."

Preposition / noun phrase / sentence

The trouble is in elucidating why it is so that "despite" is a preposition that sets up a contrast. How is one able to think of the relationship of contrast given through "despite" as something analogous to what "in," "by," "through," "at," locate, all of which are so much easier to imagine spatially, which we think of almost statically?

How can one think, imaginatively or analogously or otherwise, of the way by which prepositions set up relationships of contrast? We can think of that already in "across from" and "beside" ? Is it simply that one can think of a preposition as an "arranger" which places things into position, and so is capable setting up a relationship?
How is that different than how an adverb sets up a relationship of contrast?