He means that he is progressive and compassionate and forward-thinking and stands up to the man and stuff.
The way to signal LW ingroupness would be to say "signaling progressiveness", but that does cover it fairly well. I suspect the logic is roughly that our current prison system (imprisoning people for 12 years for a 1st time drug offense) is bad in the direction of imprisoning far too many people, so opposing our current prison system is good, so opposing the current prison system more is even better, and the most you can oppose the prison system is to support abolishing all prisons.
(actually there might be something of an argument to be made that...
Another month, another rationality quotes thread. The rules are: