The problem might be you: are you trying to convince random unknown people on the Internet to change their minds? Absent knowledge of their true motivations, beliefs or biases? Don't bother with "nicely" but don't be critical either; just be factual - people always hear what they want to hear, and that's not actually your problem.

It is an order of magnitude more efficient to simply move on to the next person, because there are always more people.