I've been feeling conflicted about anonymity lately. Like you, I've spent a lot of time on anonymous imageboards, and like you, I feel repelled by identity-defined social media.
But I think about how in an old society, before computers, and before the large conurbations that modern cities have become, identity and reputation were vital parts of the way you related to people. The society was a fabric made up of the individual reputations and relationships of the people who composed it. By preferring anonymity, am I copping out of the true defining characteristic of social interaction?
I think you hit on a good point. It's the solid and permanently tangible record
of everything you've ever done on social media that's repulsive. You may change, but to anyone who cares to scroll back to five years ago, you will always be an intolerable teenager. Your identity, your reputation can become frozen in the past by nature of its instant recall-ability.
And I wonder if people are censoring themselves because of this. Teenagers, who don't know how to live without it, are they aware of the large time-world they're speaking to when they post with an identity? Do they bow to peer social pressure more than they would if they could speak only to a small group of friends, and have those words "disappear" as soon as they're said?
I don't know. I'm worried, like you.