OP, you came on here throwing knives at your girlfriend, blaming her for the whole situation, ascribing malice to her actions and painting yourself as a blameless paragon of virtue.
And then you are surprised that people threw those knives back at you to defend her.
It’s entirely possible the pregnancy is just an accident. One which could had been more likely to be avoided if you had taken a larger part of the shared responsibility of contraception. And it’s entirely possible that the conversation has become bitter and angry due to your initial reaction (anger, hurt, blame) rather than because your girlfriend is a bad person.
If you’ve said you don’t want a vasectomy in case the girl of dreams comes along and wants a baby, but then outright reject the possibility of keeping an unplanned baby, you’ve basically told your girlfriend that it’s not that you are totally opposed to babies, but that you judge her unworthy.
I think your anger at your girlfriend is misplaced. You are actually angry, and right to be angry, with yourself. You could have taken extra steps to make pregnancy even less likely and didn’t take them. She did take some action, it just wasn’t sufficient- no single form of contraception is ever reliable enough for that. You didn’t take action.
You let yourself down. The mature and morally upright thing to do would be to shoulder the consequences and get on with it, whilst working through your anger with yourself in a way that doesn’t harm others. Not to try to take out your anger with yourself on someone else who actually did their share of prevention.
By the way, when you are angry with yourself, taking it out on someone else won’t solve the anger, it will just intensify it. You weren’t and aren’t being responsible for yourself and you will end up hating yourself for it.