Or maybe it's all just a hopeless mess.
Anecdotally, there appears to be a variance in the average intelligence of Slashdot's comments that is related to the USA academic year. Slashdot gets dumber in the early Fall, recovers somewhat around the time of study for mid term exams, gets dumber during the Winter break, etc.
This suggests that one way of improving Slashdot would be to prevent persons under the age of 25 years from making comments. But that might be difficult to enforce. Blacklisting persons who are enrolled students in certain schools (Princeton, Yale, Stanford, etc) would also be effective, but also difficult to enforce.
An enforceable policy would be to start all newbies with a karma score of -1 (negative one), to be increased automatically on the 3rd anniversary of their join date, or by merit of their posts (the usual). Most of us who care enough to not want to see the garbage could filter at zero and above-- which should be the default anyway.