A guideline I use is a response limit. This means if I initiate a post and someone comments with an argument, I will respond once. If they come back with more arguing, I don't continue. It is not easy to do this as it will feel like resigning. But if I've made my point twice, once in the post and again in that first reply, there's no more to say.
Here is the most important point. You are not writing, replying, commenting, etc. for the individual who is engaging you. You are writing for all the silent readers who are quietly interested in what you are saying.
I like this concept. If we have something meaningful to contribute, it is good to share, and perhaps follow-up with clarification if required, but beyond that, discussion with strangers invites conflict.