You can be either. I personally never ever discarded anyone. I'm the one who got discarded. I gently disassociated myself or didn't act like i wanted anything at all and didn't allow things to progress into a relationship. I got rejected probably 2 times in the past and more recently one rejected my friendship and then completely ignored me like invisible garbage. Got discarded 2-3 times. I don't even remember exact numbers it was long time ago but no more than 2-3 times. It was for the better because i was young and couldn't imagine how my life would've turned out had any of them decided to keep me. There's always someone better. I'm never good enough, never perfect.
Is it part of our purpose to be used? Nobody used me in any way, nobody took advantage of me. Being with me, giving me time of day wasn't really using me as i enjoyed being with them more than they enjoyed being with me. Whatever i chose to do for them they didn't ask me. The only emotional pain they caused that will never go away is they were with me because they had nobody better at that time. As some say, they weren't my anything. It was simply my turn to be with them and their turn to be with me. After me it was someone else's turn. And so on. I can understand some/many women where i am use men for money and material things or physical labor. That's abuse. Wasn't the case with me.
Yes you can discard and not care. I wish i could do to them what they did to me but can't go back in time. I can't even approach the more recent one who doesn't give me time of day anymore. She rides the carousel 1-3 times with a new tinder date every week. Then discards them. I guess it's normal and no big deal. We always tend to look for something better. Better car, better house, better gf, better wife, better food, better country, etc. We are disposable.