AITA for getting 3 co-workers fired for making a hot list?

A bunch of people from my department at work went for drinks on Friday after work. Everyone was having a good time and there were about 20 of us there (from about 30 people in our department). I go to the bathroom, and as I am about to exit the hall to the bathroom I hear my co-worker say my name from around the corner of the wall. Perhaps I shouldn't have eavesdropped, but curiosity/suspicion got the best of me and I did.

I overheard a conversation of three guys in my department making a "hot list" (they actually referred to it as that), which involved ranking every woman in the department from first to last. I was upset and disturbed. I was quite friendly with 2/3 of the guys, actually. Yesterday morning I tell HR and they state that they have a zero-tolerance policy for actions like this. All three men were fired first thing this morning, and now I feel terrible.

I hated the way they were talking about women, but I didn't think they should be fired. With that said, we work for a large company that I know takes complaints like this seriously, and would not really miss these 3 guys, so deep down I suppose I knew it was a possibility when I complained. Nobody knows that I am the person who reported them, and I've overheard people say that the person is a "snitch". I'm wondering if I should have just confronted them at the bar and told them how it made me feel instead, but at the time I didn't feel comfortable doing that. I especially feel bad because I had a fairly good relationship with two of the guys.

AITA?

INFO 1: It was not a formal work event, but our supervisor organized everyone going out for drinks

INFO 2: A lot of people are insisting that I am upset because I was low on the list. I tried to avoid making this the focus, but with all the comments I feel like I have to address it. I was high on the list, and was not offended about my placement; I was offended about the fact that they were making a list in the first place. I hate that I even have to write this

ETA: wow this is just about the most toxic thing that has ever happened to me. I came here for judgment on whether I am an asshole in this situation, and I have gotten numerous personal messages calling me ugly, a bitch, fat, a nazi, psycho, etc. I really think something needs to be done about this sub, although admittedly I'm not sure what, because I can't believe this is the response for somebody using this sub for its intended purpose

update: I will be speaking to HR about the messages I received