I think that's a part of OP's point. After that, if you wanted, you could go away to college and buy normal clothes and reinvent yourself completely.
Nowadays, if you're a person who agrees for whatever reason is a shitheel, you're that same shitheel forever, and the inertia required to overcome that is greater.
You're right in the sense that the internet also allows to find sympathetic others, but that doesn't shake the stigma, merely exposes it to more people. (Which has the added benefit of contributing to polarization.)
Howard Dean's political career was ruined and is largely defined by one poorly timed on-air scream after it was mocked by late night comedy hosts.
If you remember Lindy Chamberlain at all, it's probably as the "Dingos ate my baby" lady, whose name was dragged through the mud and went to prison for years before it was revealed likely that dingos had almost certainly eaten her baby.
Chris Jeffries was questioned in the murder of Joanna Yates.
Richard Jewell. Fatty Arbuckle. Bruce Ismay. Rebecca Black. Kevin Carter. Monica Lewinsky. The McDonald's Coffee Lady (Stella Liebeck). If you remember any of these names, it's almost certainly for something bad they were accused of doing.
I've seen studies that show that because our brains are our foremost self-defense mechanisms, they're constantly looking for bad patterns to avoid, so we remember the bad things about people much more readily than we remember the good. That we do so for faraway people with whom we'll never likely have any contact is likely low on the utility scale, but we mostly haven't adapted to avoiding it.
Actors who manage to land parts doing crime scene reenactments for true crime docudramas tend to regret them, because people at the grocery see the actors and forget they were watching television and assume he's a serial murderer.
We rely on our intuitions so much when meeting new people, and our brains hold onto negative impressions so strongly that even though you think you don't have the energy to keep track of it, the brain actually does. Perhaps not just over a disagreement, but if you form a negative connotation around a picture of someone internet infamous, cognitive bias ensures that you'll likely dislike them if you ever actually meet and they'll have to actively work to overcome that negative preconception despite us having formed that preconception based on perhaps as little as 10 seconds of their life portrayed out of context.
If you do not dislike anyone that you haven't met (e.g., a politician, or polarizing celebrity like Logan Paul or Joe Rogan or Elon Musk) then congrats, you're in the (presumably) low percentage of people who don't have this affliction. But I think it's a pretty big stretch to say that "most" don't.
Amazing to think that Donald Trump could make gaff after gaff and still, inexplicably, be considered electable. Dean made one dumbass howl and got shit-canned. MSM in action.
Also, a shame about Fatty Arbuckle, dude even got an apology from the court but still got his career ruined.
Back in the day, if you were a pathetic loser, that’s all you were, and that’s how you had to navigate life. This would force you to take an honest look at yourself and see why you don’t fit in to larger society and maybe if you should try to be different. And eventually you might become a version of yourself a bit more acceptable to society. Even if you knew deep down you were a pathetic loser, at least now you knew how to cooperate and be agreeable with others and even make friends that are different from you and not total losers. In time you would gain wisdom about life and be content with yourself.
But now? It’s quick to find so many others exactly like you, and you can feed off each others thoughts and words of encouragement, no matter how twisted. Eventually you see everyone not like you as an enemy, rather than as a person whose friendship and acceptance you seek to earn. You lose your connection to the rest of society, you find yourself increasingly unable to relate, and find yourself spending your days seething with hate at the society that you feel has nothing to offer you, filled with people you’ll never give a fuck about.
Personally, it's a net positive for me.
Not just that, it's one of the biggest themes in modern American fiction before social media. Most of PK Dick's work deals with the opressiveness of middle class culture, mental illness, people who don't fit in and how these things overlap. You had Fight Club or Taxi Driver on violence and isolation particular of men, or American Beauty on the conformist and almost totalitarian nature of the suburbs, etc. It's been a major topic in American culture for decades.
Social media is small town gossip, at scale.