Nagarjuna does not do all that brilliant work simply to establish a crude subjective idealism.
You didn't see where I explained how this should not lead to idealism? Idealism is what you prematurely jump to when you don't have a full understanding of the teaching.
When a rock is apprehended, it is signified "rock" and exists as a dependently designated "rock" in conventional reality. Conventionally, it depends upon this designation + causes + conditions.
Take away the designation what do you have left?
Nothing? So the rock disappears??
"Take away the designation what do you have left" is a bad question. Stop before
your assumed "rock is apprehended", not after. That statement is the initial mistake. Your apparent causes and conditions are also just as illusory. The true cause and condition is no external element whatsoever.
If dependent arising is denied,
Emptiness itself is rejected.
This would contradict
All of the worldly conventions.
If there is essence, the whole world
Will be unarising, unceasing,
And static. The entire phenomenal world
Would be immutable.
It seems you want to deny the dependent arising of form.
Not deny, but simply point out that dependent arising in Mahāyāna teachings is not the same as classical teachings which state the causes and conditions of phenomena arising and ceasing are an interdependence of other external elements. That's a very elementary understanding.
Mahāyāna teachings should not be read in the classical sense. Mahāyāna teachings state that such causes and conditions of an external material realm are just as illusory as the apparent forms which appear within it.
The point of classical teachings of dependent origination is to deconstruct wholes into parts to show there is no eternal element or self within them, in order to cut grasping. The point of Mahāyāna teachings of dependent origination is to show how even those apparent parts are illusory, which lead you back to a deeper cause; into consciousness, which is later also relinquished, and one arrives at the wonderfully enlightened bright mind.
Where is anyone denying that there is some form there?
Not denying there is an appearance of form, but form as an actual external element, that is denied all over Mahāyāna teachings.
Take the Buddha in the Śūraṅgama Sūtra, Chapter 9 for example:
"Contemplating the cause of the form skandha, one sees that false thoughts of solidity are its source."
Or Chapter 3:
"Whatever manifests does so in compliance with karma. Ignorant of that fact, people of the world are so deluded as to assign its origin to causes and conditions or to spontaneity."Whatever
manifests.. karma is consciousness.. external causes & conditions are illusory.
Probably the most famous of all statements in the Mahayana is very explicit: Form is emptiness; emptiness is form. Form is not other than emptiness; emptiness is not other that form.
Yet, how amazing it is that people still make that statement say what they want.
"Form is emptiness"- there's nothing there.
"Emptiness is form"- yet there is an appearance nonetheless.
To repeat the Śūraṅgama Sūtra;
"Ananda, suppose a person with clear vision were to gaze at clear bright space. His gaze would perceive only clear emptiness devoid of anything else. Then if that person for no particular reason fixed his gaze, the staring would cause fatigue. Thus in empty space he would see illusory flowers and other illusory and disordered unreal appearances. You should be aware that the form skandha is like that. Ananda, those illusory flowers did not originate from space nor did they come from the eyes. In fact....
....From this you should understand that the form skandha is empty and false. Fundamentally its nature cannot be attributed to either causes and conditions or spontaneity."