I hope this helps. Some things I've learned:
IRL, you can only control your own behavior; the same is true here. If you believe framing a comment in a certain way will guarantee that you won't be met with defensiveness or worse, your expectations are unrealistic.
Be direct and polite. Remember that people can't read tone from a short sequence of written words, and no one likes to be corrected in public, so treat someone as you'd like to be treated (please disregard this advice if you like sarcastic mockery as a response to your own answers!)
If someone is flat out wrong, you can simply state what you know to be true, adding a link. Then walk away knowing you've alerted the next reader to a possible inaccuracy.
You can ask the user an honest question if you're confused. Most people are happy to explain. I can't remember this ever going wrong for me (other than egg on my face if I was wrong), though I'm sure it has.
Avoid rhetorical questions.
Avoid snark. If you feel snarky about an answer and show it, then expect an attack. What's good for the goose is good for the gander.
...at best a blustering and unconvincing counter-argument...
It takes two to spar. You've made your point; if you don't like to spar, just walk away.
Assume the best about the user. You don't know the person you've directed the comment to.
Remember you can just DV, flag, or move on.
From experience (and advice from others on SE for a longer time), the best thing is to make your comment and move on. Drop it. Don't engage. It's perfectly OK to not reply to a comment challenging yours in an unproductive manner, if this is what concerns you. Flag something if someone answers you in an offensive manner.
Given that excessive courtesies are discouraged on Stack Exchange...
They are? I mean, I don't start my comments with Dear Sir or Madame, etc., but I never saw a prohibition of common courtesy, even in excess (except for welcoming new users, and that varies from site to site.)
Things I know in my head but have yet to put into practice consistently:
Don't argue with people with fragile egos or certain mental illnesses.
Good luck. I've briefly read over some of your comments and you don't come across as offensive to me at all. I don't think this should be a big problem for you here.
(I've made a lot of mistakes. If I've ever given you a hard time, I've forgotten, so please just accept my apologies.)