I try to be nice. Some people are just begging to be abused. Sensible and civil conversation would be great. I recently got an e-mail from someone who saw me on here and after a few messages back and forth she told me it was great talking to an American who wasn't so easily offended. After her next couple messages it became increasingly clear why the Americans she spoke to became offended, as her messages were full of anti-American elitist garbage.
With these kinds of people you have a few options. If you are extremely level-headed and patient, you can try to talk sense to them while remaining nice. Often they will try to shout you down with their baloney if you do this, so it can be a frustrating and unrewarding approach. You can try to fight back, which typically leads to unproductive flame wars. Or you can just ignore them, which is what I chose to do in this case.
I think in person people are both generally much nicer and more polite where they can see the people they are interacting with, and they are also much more likely to want to avoid confrontation. The chit chat that goes on in normal everyday conversation is usually so much mundane crap that nobody is going to get offended, usually by design. Social convention has evolved this way to avoid precisely the kinds of discussions that dominate the online world, where people feel empowered to say whatever they feel like because of the anonymity of it and the power the internet gives them to walk away from any argument. Most people who contribute the most venom to online discussions are those who are not terribly invested in the community they are spewing into- the so-called trolls. They get off on agitating and it doesn't matter to them if they come in and do a couple drive-by shittings that get everyone riled up because they can just move on somewhere else. This usually doesn't happen in person, where the people you interact with are friends, family members and coworkers that you are likely to have to deal with in the future whether you want to or not.