You can't argue with most liberals... especially using the arguments you most frequently see used by libertarians..
rights? who cares... we need people to eat and have healthcare
efficiency? who cares... at the cost of someone's livlihood...
There are some you will never be able to reach, but there are those who you can. The easiest to convince, are actually some of the more genuine liberals and socialists. Those who actually believe what they claim.
When you point out to a teacher that they get their money from property taxes that keep going up... and that is taken from poor people... they start to get a clue that when they get a pay raise, it hurts people.
When you mention that inflation erodes savings so a poor person cannot save... and is thus dependent on borrowing for everything... thus empowering huge financial firms above the poor person... they start getting a clue about printing money and debt.
When you mention to a labor supporter, that unions prevent poor people from getting access to jobs by making sure the one advantage they have (cost) cannot be used, and unions tend to run in the family, thus further excluding people... they start to get a clue.
i've found genuine socialists and liberals very easy to get onto the libertarian side. No surprise, since many early leftists movement were anti-state... until they took over the state...
