For all of the ways in which Twitter has evolved since its creation, in 2006, when it was known as “twttr,” what has not changed is how profoundly Twitter relies on nowness. Nowness is not simply newness, or the new: the question Twitter used to ask of users when they went to compose a tweet, “What’s happening?” is a direct inquiry about the state of now. Twitter’s intense focus on immediacy has manifested in many small ways—for instance, users can only see their three thousand most recent tweets (and the service only recently added the ability for users to download their entire Twitter archive and conduct searches of tweets from the past). But, most important, when a user logs into Twitter, what they see is a raw, unfiltered stream, with the newest content at the very top. Facebook, by contrast, shows users a curated feed; the top of the feed is not what’s new, it is what the algorithms think is best.
In the aftermath of the Reddit and Twitter-driven vigilantism over the Boston Marathon, there've been plenty of calls for revisions to the manner in which Twitter functions as a firehose for information.
Loudest amongst these was Mat Honan's call for editable — and therefore accountable — tweets. In principle, the notion of higher accountability makes plenty of sense as you'd be able to address your mistakes as items of information began to spread.
In reality, however, it would add an element of retroactivity to Twitter that's utterly ill-fitting of the so-called "nowness" of the platform. Twitter thrives upon now and not upon what you once tweeted. Accordingly, it's what you say now — whether it's the acknowledgement of a mistake or the act of reporting a news item — that matters.
Perhaps there's no easy route to retroactively address inaccuracies in tweets, but that certainly does not discount accountability. If you get something wrong, address it and own it as you would in real life.
Sure, it'd be nice if we could edit virtually anything in our lives for accuracy, but that's just not the way life, or accountability, works. The only tool to combat and avoid such problems is self-restraint and basic intelligence.
If you're worried about spreading misinformation via retweet, then don't retweet. If you're worried about getting a fact wrong, wait a moment to check before you tweet in the first place.
Twitter isn't broken and it's not in need of such a feature. People just need to adjust to this consumptive vacuum of information and learn some level of accountable maturity before engaging.