I am a very passionate person who is loud about their opinions, so I've had a significant number of arguments with friends that were so heated we stopped talking. At that point they may have considered me their enemy, but I always expected that eventually we would talk it out, make up, and be friends again. I didn't really have enemies, I had friendships that were on hiatus -- though sometimes acrimonious hiatus. For all but 2 friends, this has been true.
A few years ago I had an interconnected group of friends. We invested in maintaining our friendships the way many people invest in their romantic partners, and we invested in us as a group. We were intimate, and I approached all these friendships with the goal of lifelong connection. I expected that if someone hurt another person, they would approach that hurt with integrity and a desire to help them heal.
Then one of the friends, Cora*, hurt another in a profound way, and when the hurt person, Alex*, expressed this pain and asked for help, Cora just ghosted for months. I thought this was mega fucked up and I stopped investing in Cora, but did not confront them because Alex didn't want me to.
I talked to another person in the group, Erin*, about it. Since Erin was close to Cora I felt like it was important to explain why I was not going to be investing in them anymore. I got permission from Alex to explain what happened and while we were in person, Erin agreed that Cora behaved unethically and that it was fucked up that Cora flaked out and left Alex in painful limbo for months.
Later, Erin defended Cora's choices and denied that the worst of what Cora had done even happened, despite being given proof. She decided to deny the truth and cut me and Alex out of her life rather than face what Cora had done in an honest way. To me this is a profound betrayal, and I am disgusted by it. After that, Erin was not a friend nor even a friend on acrimonious hiatus, but an enemy.
If you want to be my enemy there is an easy recipe for it: choose maintaining your relationship with an unrepentant abuser** over demanding ethical behavior from them. Or just be an unrepentant abuser.
Still, this status is not necessarily permanent, because I accept people growing and changing over time. But Erin and Cora would each have to put in a huge amount of effort and frankly, I don't ever see that happening, especially given their shitty lack of effort when it was fresh.
I lost one of my best friends over this, because of their ties to Erin. That is the one thing that still hurts, though I understand why they made that choice. Being friends with me was more work, logistically, and less reward, socially, because I didn't have ties to all the cool people.
Nowadays it is really important to me that I only build friendships with people who are willing and able to hold their friends accountable for hurting anyone, even a stranger.
*names have been changed
**abuser of people other than you, that is: I know it can be nearly impossible to leave someone who is abusing YOU.