tl;dr: Peer pressure is a normal and healthy part of communication. You use it in this comment and it is baked into this website through the karma system. Using it for disagreement and not just conformity is important to keep groups attached to meaningful values. I don't think "What the fuck is wrong with you" is unfriending, and I think that sort of harsh peer pressure can be and was justified by its context. I think you're mistakenly arguing against peer pressure in general and absolute terms when your issue is specific and one of degrees.
Indeed it is a poor tool for determining whether the intended goals are worthy. That's what the entire rest of the comment that people have been systematically ignoring is for. Condemnation is the sledgehammer in a suite of construction tools, itself unable to tell whether it is in the right place doing the right thing, but justified (or not) by it context.
And, like I said, upvote karma is peer pressure. People can see at a glance how many people will see something and how many people agree with it in a way that becomes a self-fulfilling Keynesian Beauty Contest. If you truly believe peer pressure is wrong, then the lemmy architecture is fundamentally hostile to you. If an invective adds toxicity to the soil, then the soil here is full of lead already.
But the reason civil debate between neutral people has so little part in progress is because nobody is truly neutral, not because so few people choose to be civil. Marxism works well as a model for society because people are by nature hypocritical. Philosophy, culture, and social groups are a layer of topsoil, vegetation, and human structures covering the mountains of what we think benefits us personally over the course of our lives. Argumentation can redirect superficial flows, which occasionally allows for a key watershed moment where your way of life is redirected onto another plausible course, and that course over time changes the geography. Sometimes that redirection means taking a sledgehammer to a wall.
I agree that it is easy to cooperate with people when you only care about liking and trusting them. That's how you get social groups and movements that are entirely detached from reality, a bog of stagnant water. If you want a social group to have sensible, actionable beliefs rather than descend into circlejerk, you need the members of your group to be systematically willing to cause offense when it improves the group's ability to interact with the outside world. And for them to be systematically willing, you need to react positively to them doing so. Otherwise, over time, the detritus and resistance builds up in that channel and it clogs up, and the flow becomes stagnant or goes elsewhere.
When you ask me to choose people liking and trusting each other over processing disagreement, you are not opting out of peer pressure. You're simply using (soft) peer pressure to enforce group norms that are about cameraderie rather than beliefs.
I do not consider the application of peer pressure to be outside the scope of good faith argument, otherwise I would not be on this website with its karma system, I would not reply to you when you talk about whether or not people will like me, and in fact I would not be able to communicate with anyone. I don't feel like @solo is an enemy or an unfriend, just someone who needed a wake-up call.
I don't see saying "what the fuck is wrong with you" after someone says something horrendous as abusive. I would personally genuinely appreciate that kind of clarity if I said something that revealed a fucked up underlying attitude, when accompanied with a sensible explanation. It's an emotive way of saying that you're noticing something deeply wrong with someone's worldview, and opens up the talk in that context. And honestly, I doubt you or others on here are unfamiliar with that sort of usage and don't partake in good-faith invectives yourselves on occasion.
Honestly, I think that maybe y'all have talked yourselves into a corner arguing against peer pressure and invectives in general when you really only disagree with how (and whether) it was applied in this instance. I could be wrong, but that's my impression.