Replying to Political beliefs amongst friends. Argue or let it go?

As you can already tell by now I am a bit right of center on the political spectrum, or maybe that is an under statement.

I have noticed that we conservatives and liberals are always pretty quick to share our opinion when a sensitive topic that relates to liberal vs. conservative points of view occurs, but do we do that because we don't know each other, so why care?  But then why do some of us put so much effort into instilling our beliefs in those threads with each reply?

If we are with friends and someone says something ignorantly liberal or conservative do you correct them or just let it go? To tell you the truth I usually always let it go.  However we go through so much effort on this forum trying to inform people about the wrongs of their political belief, even when we don't even know the person at the other end of the argument. 

So then why don't we go through the effort of trying to inform a close friend about something that they are considering in their argument which would nullify their political opinion?

Is it because society has deemed it a social taboo and that it is better to leave the person be and let them find out on their own?  I guess I could say I feel that way, but does anyone else do the same thing and not even bother most of the time?

I guess this thread probably isn't the best place to put it yet alone on this kind of site, but hopefully the minority outweighs the majority if you know what I mean.