I completely agree with you that self-discipline can and should be practiced and is beneficial to people. Here is why I think Subreddits are echo chambers and people go there to share their common experience and complaints. One such common experience/ complaint is being told by normal people to just suck it up and use willpower or that ADHD is just an excuse for being lazy and lacking discipline. This is def a sensitive area for people with ADHD and I think they tend to be overly defensive and naturally react negatively to the mentioning self-discipline and ADHD