Yes your frustration is totally understandable. It is a very heated topic and a lot of bad faith arguments are thrown around.
Sometimes I remind myself not to hope that the person I'm replying to will understand my reply or acknowledge that I'm right - instead I post my reply for the lurkers to read, who are far more numerous. The lurker has not publicly said anything so their ego is not fixed on defending their position and they are more likely to receive what I contribute with an open mind.
With this wider context, the goal changes. When the target audience shifts to the readers then there is no longer a need to continue a long back and forth discussion (the person replying to me will never change their mind anyway!) once I have made my point clearly. It's ok if the other person has the last word if by having it they discredit themselves by demonstrating a closed mind - the lurkers will see it.