Yup. The 140 character limit is twitter's worst feature. It's difficult to have any substantial discussion or nuanced debate in a stream of 140 characters or less.
Brevity is indeed beautiful, but usually only after your quip has been long considered and pared down from a much longer form of expression. The brilliant aphorists of the world didn't just crap out their sentences of brilliance--they toiled on them (Nietzsche has quite a few good maxims on this subject). Services like twitter make it easy to react and to throw your thoughts out there without engaging in any reflection first. Then it's easy to respond immediately with some follow up nonsense once someone disagrees with you.
It shows you how the medium really does impact the message to a huge extent. Imagine how different it must have been composing letters in, say, the 1700's as opposed to writing tweets. By the nature of the medium itself you were almost inevitably likely to ruminate on your subject and think about it more deeply in the time between your letter's arrival to its destination and the subsequent appearance of a response. Nowadays you have feedback in seconds, and most of the time it reflects the minuscule amount of time and consideration behind it.
That's not to say twitter is all bad--the format has its benefits too--it just certainly has affected the way and the amount of time people devote to thinking and questioning themselves. In general I think having the ability to consider things slowly and to take one's time may only grow all the more important in the future.