Some of it has to do with what you believe.
"I am 100% for abortion, but I am still for Ron Paul as it is not a primary issue right now and his personal take on abortion is fairly meaningless, since he wants this to be decided upon by the states. Ron Paul is the only candidate that will get us out of the wars, end the Patriot Act, and fight against the corporate and banking interests in Washington."
(If they argue that he is corporatist, etc) "No, don't confuse him with the scumbags at the CATO institute. Ron Paul doesn't work for the Koch brothers. If he did, Fox News would love him. Most Ron Paul supporters consider Fox News, with a couple of exceptions, to be the biggest liars in the media. Ron refuses to even go on Bill O'Reilly's show. This is why there is a groundswell of support for him. This is why you see his signs and bumper stickers everywhere, but everyone in the media wants to marginalize him. Ron actually names the military-industrial complex, he goes after Goldman Sachs, and he wants to end the Federal Reserve."
I have a lot of experience with left-anarchists, and that is partly my background. A major portion of them don't vote period, so while you could have a good conversation with them, it won't mean a lot if your only goal is to get votes for Ron Paul. Many of them are very cool, though. The brighter ones will be familiar with John Zerzan, Bob Black, and the Situationists, and have a strong ecological/holistic perspective. The dumber ones will typically identify as anarcho-syndicalists, and they are viewed as sort of a joke by the other anarchists. They are like Marxists without the intellectual veneer.
Marxists/RCP'ers are more volatile and strident. These guys can be a waste of time, but it is interesting to see how they view the world.
Amongst the more moderate left-wing crowd, the types who look to Chomsky and Michael Moore, you can mention things like how Dennis Kucinich said back in 2007 that he would have chosen Ron Paul as his running mate if he won the 2008 Democratic nomination. They can look it up on the internet. That is how much Ron's integrity and common interest in ending the wars, the Federal Reserve, and corporate interests meant to a genuine progressive. Ron Paul agrees with Chomsky that our problems around the world arise from blowback, from the hundreds of thousands of people who have died due to our wars and our sanctions. He has been saying this since the 1970s.
Be prepared to rip into Obama, and go into his ties with Goldman Sachs, Monsanto, and others.
Btw, I would recommend watching the interactions that Adam Kokesh has had on his Youtube channel with the OWS crowd. It is pretty interesting.