No one is telling you not to follow your heart, but debate using your head, and accept that sometimes, you're just going to be wrong. We've all been there on here, and we've all gotten a little too heated, because we all inherently care about we're discussing, so that's gonna happen. The key is being able to pull yourself back from it, and no when you've said your full piece on a subject. Their doesn't really have to be a winner and a loser.
There have been several times where I've walked into a debate talking about what I've seen of the oppositions position, and trying to bring across that perspective on the argument. Usually, I reserve this for when I feel a particular line of thought isn't being represented, and should be talked about.
My biggest thing is making sure not to tell people how they feel. This is probably the biggest debating no-no there is, because there is not a single person on this Earth who likes being told how they feel, and so all that gets accomplish is getting their blood up, and the debate starts to go away. It's also often used as a way to slight someone in a backhanded way, using it in a pejorative manner to evoke an emotional response.