I have read articles written about why we should be able to modify existing tweets, but I haven't been able to find anything substantial about why we can't.
My initial thought was that edited tweets would compromise the transparency or accountability of tweets. If we could change tweets, it could potentially detract from the real-time dynamic of the experience. Yet there are proposed workarounds for this, my favorite being Mat Honan's suggestion that edited tweets could be flagged the way favorites and retweets are, and the original tweet be viewed using Twitter's Cards function.
Is making user actions nonreversible (outside of deleting and reposting, an action that also affects the pace of Twitter) a tradeoff for effecting a live experience? Is it a constraint that is hanging around from Twitter's SMS days? I'm looking for data or research that supports Twitter's approach in not allowing tweets to be edited.