I don't actually have a Facebook, and I'm not active on any other kind of social media. At least, not to the extent that most people are. In real life I have a small group of friends who I love and trust completely, this group consists of around 6 people. Then I have all sorts of acquaintances and people I don't mind spending time with, although I wouldn't trust them with my deepest secrets and so on.
I think the first thing to keep in mind is that you should never "Fight" with your friends. No one is ever going to win if a debate or discussion devolves into a fight. That's why I try my best (And regularly fail) to not engage myself in online discussions. More often than not, it becomes a mud-flinging contest and people show their worst sides because it's much easier to be cruel on the internet when no one is looking you in the eye. Some people are just toxic by nature, deliberately trying to incite rage and hatred in the people debating by making outrageous claims that they probably don't actually believe anyway.
When I discuss sensitive subjects with my friends and we disagree, I do as any sensible person would I feel. I lay out my opinions and my beliefs, I use all the facts I have at my disposal and I make sure to tell the person/people I'm talking to that I don't know for sure how something works if I indeed don't know. If they disagree I challenge them on that position and try to insert some clever metaphors and theoretical examples that aren't hyperbolic, but that they can perhaps better relate to and thus see how they perhaps don't actually agree with what they thought they believed.
If they are adamant and can back up their opinions, I leave it if they can justify their position on a particular matter or listen if I think they've got a point I didn't consider myself.
If someone goes "TL;DR" then they obviously don't care enough to engage themselves properly in the debate, and it's just not worth debating with them. I'd imagine those are the same people who, if discussing while face-to-face, would eventually go "Whatever.." or say "Well, that's your opinion!" and no longer be constructive.
On the other hand, there is a bit of a bias here: I thrive on debates and I love discussing everything from political and philosophical issues to how I thought a particular movie that got critically acclaimed was actually awful. I just love talking. I'm sure some people here who I have talked to in other debates might have their own opinion on whether or not I'm any good at it, but I enjoy it.
But it is so important that everyone is comfortable during a debate. You can challenge people, and people may feel uncomfortable expressing their actual views on something, and that's okay. But the moment anyone gets enraged or starts being threatening, disrespectful or patronizing, that's when the debate is sure to either dry up or turn into something ugly.