It is fashionable to consider indifference as a sentiment, even as a "wise" sentiment, an approach possibly drawn unconsciously on Greek stoicism and also in some sense on the teachings of Buddha (no desire, no suffering). I have even heard that indifference is the opposite of love. One could treat this assertion in an ironico-comical way by having the big drum of the absurd resonate: "If indifference is the opposite of love, it is also the opposite of hate, and thus love and hate, having the same opposite, are one and the same thing". I'm not sure that this farce is so absurd in some cases.
The same approach, this time with the pretension of gunning down metaphysics, wants firstly to look at nothingness as the inverse of being. But nothingness, in other words what doesn't exist, is no more the inverse of anything than the inverse of itself, since it doesn't exist! It is already not convenient to signify being, but the representation of "what is not" frankly makes one giddy. That's probably why this approach is in style: it procures a sensation, not unlike that of the Kingda Ka roller coaster, of which I have always thought was the poodle's chance of having an intuition of being.
Yet, given that indifference is the absence of sentiment, it is the non sentiment par excellence! Exactly in the same way that silence is not the inverse of noise but the absence of noise, illness the absence of health, and finally evil the absence of good, and in no way the inverse. That's a whole other ball game! And this is fortunate, for if in Swiss cheese the holes were the inverse of cheese, needless to say your cheese would have a rather odd taste!
Some buffoons, to maintain willy-nilly the primacy of nothingness and negation, have not been loath to affirm that noise was the absence of absence of noise. Jean-Paul Sartre has shined singularly of an intergalactic cretinism on this matter, leading several generations to a suicide of their intelligence, for what falls first in intelligence is being, not nothingness!
To get back to "indifference", the final prestidigitation consists often in assimilating indifference (or apathy) to contempt. But contempt is an active form of sentiment, model derived from hate with specific qualified accessories. This error is not that of Buddhism, for apathy assumes with Buddha the form of a certain compassion. I admit for the rest that I have always thought that Buddha was more of an artist than a mystic (contemplating the "chose en soi"), which seems to be confirmed by many westerners whom at one time or another were seduced by Buddha (Nietzsche, Cioran), thinkers primarily on a quest that art save man and the world, at least from suffering.