Make Writing a Habit
Writing is not publishing. If you conflate the two you might not write at all. Having a place to write is as free and easy as:  mkdir ~/thoughts

Now, after you've replied your quick counterpoints to someone on HN, whip out the text editor and  vim ~/thoughts/why-writing-is-not-free-nor-easy

Go and expand on your thoughts on the subject there. It doesn't have to be prosaic, some simple bullet points that encapsulate the main ideas are enough. You can revisit later for an in-depth or progressive analysis. Do that even if you didn't actually reply to anyone, but felt merely like jotting down notes about your take on the matter. Write your own thoughts on stuff that people share in real life, on HN, youtube, facebook, etc. Observe a curious phenomenon and write a single line about it in a file. It's easier than Twitter. With the latter you worry about presentation, whereas the former lets you capture the main thoughts quickly, without worrying about form.You don't have to publish. It's just writing, it's for you first and foremost. Over the years revisit, refine, and expand on your thoughts. Write articles over the course of 10 years. See how clever or ignorant you were 5 years ago. Allow yourself to laugh at your own jokes or to delete some posts in embarrassment. Let your mind be changed as it's meant to, safe from judgment. Some day you may feel wise enough and ready to share some selected pieces that have remained constant all throughout.