The antagonism is from effectively calling them immature (and thus implying that their opinion is coming from a place of naivety) and placing yourself above them. This is a pretty standard insult that people use to try to be persuasive.
I suppose you could say that posting that insult itself is so immature that readers should recognize it as a joke, but I suggest that you should try to stay away from sarcasm when posting in online forums. It can be quite difficult to detect the sarcasm of a bunch of people you don't know.
I could end my post by sarcastically saying "don't worry, you'll learn what a joke is when you grow up", but hopefully you can imagine how some people would take that as a genuine insult rather than a joke. Though it would be punchier ending.