You make a good point. Part of the problem with Twitter when it comes to discussion is that it does not lend itself to drawn out lengthy presentations, but the opposite. And in addition, it allows you to throw mud, unsubstantiated, as truth.
It's like "yo momma" jokes. Whoever is quick to wit with sharp tongue wins, and merit is disproportionally disregarded.
Almost every medium lets you throw mud, sans substantiation, to great effect.
Limiting mud-throwing to 140 characters isn't effective anymore than allowing more than 140 characters of mud conveyance.
The problem may be that people need to be convinced (one way or the other) now in less than 140 characters, in which case we're all doomed, as very few stories worth telling can be told in <140 characters.
Drawn out - or reasoned, moderate, thoughtful, civil, researched exchanges - are almost a thing of the past. No one has time for that kind of luxury anymore.
It's like "yo momma" jokes. Whoever is quick to wit with sharp tongue wins, and merit is disproportionally disregarded.