There is also the idea (that I think is a responsible thing to do) that will have to tell people you are talking to that you may not have looked in to whatever they are bringing up and you are not really the person to expect informed conversation from. Some people will continue talking about it and it's up to you whether or not you want to try to engage in the conversation beyond the courtesy acknowledgments. However, I find it a disservice to myself and the people I am talking to to try and interject an uninformed opinion or data point.
Ultimately, focus on those things that are important to you. Do your homework on those things. Recognize when you do and don't know something and don't be afraid to stop talking when you don't know something. Be willing to stop and listen, and don't go in to a conversation that you are informed in expecting to change minds.