Why the quotation marks round the word debate? Simply because so few people who enter into them online follow rules of debate, assuming they even know what they are. A debate without rules is an argument.
It's going to happen, especially in certain areas, politics and religion especially. There are people who get all bent out of shape if somebody "starts being political". I've seen some very good comebacks to that, but the thing is, if you have a place online that is yours, be it a blog or a Facebook page, or whatever, you have the right to put whatever you like on it. Even if it is deliberately offensive. That's your place.
On the other hand, if you publish (because that's what it is) something provocative, then you are essentially inviting comment. If you don't want comments on what you publish, don't publish.
If you desire a respectful audience, then select who sees it. Choose your "friends" wisely.
So, having published to whomever, be it a tight little group, or whatever random people Google search engines bring to you, what can you expect?
The truth is: anything. Not only will your readers have a wide variety of opinions, they will have a wide variety of attitudes too, which is a different thing altogether. What we often forget, among those who read your thoughts will be:
1. Stupid people. It is possible to be able to read and write, even write correctly, and still be stupid. Stupid is not a simple lack of intellect or academic skills. No, no, no. There are stupid people out there with PhDs. Stupid is a deliberate attitude, it involves a closed mind. This unwillingness to learn often leads not only to them saying things that display their lack of knowledge, but to them not caring that they are talking out of their bottoms. Stupidity is a cycle, downwards.When stupid people respond, not only do they get facts wrong, they generally have a bad attitude too.
2. Crazy people. Not everyone who is crazy is diagnosed. Some forms of crazy are such that the person is able to lead a life within the broad range we call normal, get an education, hold down a job, have a bank account, pay bills, etc, which allows them to have internet access. But the crazy comes out very quickly in this perfect arrangement of anonymity online. It gives them an opportunity to share their delusions. Conspiracy theories are just the start of it.
3. Liars. I forget this one all too often. If you are an honest person it's very easy to overlook the fact that some people simply make stuff up. If I tell a lie there's a good reason for it ("No officer, I wasn't there....."). These folk tell lies just for something to do, I think. I'm not really sure. Anyway, whatever their motivation is, they spew complete rubbish all over the internet, on purpose.
4. Trolls. Sometimes known as "devil's advocates", in specific circumstances, but more broadly just as "shit-stirrers" these folk are not sharing their own opinions, they simply offer the most controversial comments they can think of, so they can watch the fight that follows. Like liars, they are presumably bored, and this is a form of entertainment for them.
5. Bigots. While these can also fit into any of the categories above, specifically these folk have an unmovable attitude that they are right, and everyone else is wrong. They, of course, are NEVER wrong. What is more, most bigots take this to the next step of spewing hate all over anyone who behaves or thinks differently to themselves. All racists, by definition, are bigots. Most religious extremists are bigots. The stubbornness of the bigoted mind is very powerful.
6. The Grossly Misinformed. These people can be forgiven if you wish, as they just don't know any better. They may be young. They may have lived inside a closed society, be very insular out of fear, or simply haven't had a good education. Generally these people are polite but can repeat themselves, believing they are right. As humans have feelings, despite everything, they can get very upset when told they are wrong. On the bright side, however, they can learn. This is often your best audience, if you are patient.
7. Ditherers. Really don't have a solid opinion, and will sometimes take sides in a debate, depending on who is winning. As their inconsistency becomes obvious, they tend to get ignored by everyone, but they can still be a nuisance by echoing comments they read elsewhere, and not knowing when to shut up. Most importantly, when corrected, they don't know how to back down and can become extremely difficult, especially if they feel "ganged up on".
8. Bullies. Completely lacking the ability to take part in a reasonable debate, instead they hurl ad hominems at those they disagree with. They may start an argument, but soon realize they are out of their depth, and so go completely off-topic, to detract from their nescience. Using attack as a form of defence, they insult people, accuse them (wrongly) of the crimes listed above, and will use brute force to end a discussion. They never actually win anything.
9. Cry babies. Self-proclaimed victims and emotional vampires. As soon as they start to lose an argument, these will whine about being treated unfairly, and often utter those most pathetic of words "You don't know me!" Frequently these people start arguments, but can't keep up, and rather than back out discreetly, seek to change the focus by getting all the attention.
10. Believers. Found mostly in religious arguments, but oddly enough, not exclusively. Can be very loud in their opinions, but have nothing to back them up with. If asked for citations they often use biased or very unreliable sources, and are easily taken in by #3, as they are so credulous. When their back is up against the wall they will use "Well, that's what I believe" as their get-out clause, which others must accept, or they turn into #9.
Any, or all of these people will comment on your deepest held opinions. They won't show you any respect, nor will they ever understand what they are doing wrong. For this reason, never take any of it personally, because it's not about you, or even about what you are saying, it's all about their egos, their twisted personalities, and their ignorance.