While I agree with the thrust of your article, I think your examples could possibly use a little tweaking. Being polite definitely makes sense, but the impression I get from your examples is that being polite means dancing around the issues / taking longer to get to the point / disclaiming everything.

For example, you give the example

"I enjoyed this post a lot - thanks for that - but one thing that's tough for me is that all the examples are about martial arts [...]

The thanks for that is somewhat superfluous. Your example is already polite by starting off with "I enjoyed this post a lot."