1) People who don't actually know what Mindfulness is, other than secondhand sources, word of mouth, etc.
2) People who've tried Mindfulness, and they know a little more than (1) due to direct experience, and possibly a minister who guided them.
3) People who were born into a family whose members fervently pratices Mindfulness, teach Mindfulness to others, and promote it in public.
Now let's see why people hate Mindfulness or say it's not for them.
(1) may say that it sounds weird or foreign, it can't be efficacious, it's too abstract, because they don't know what it's about.
(2) may say that it was hard to concentrate, they kept getting distracted, the classes were expensive, they traveled too far, they didn't feel it working fast enough, it was boring, too spiritual / not spiritual enough.
(3) perhaps their family life was bad, they were neglected or abused, their family members seemed to care more about Mindfulness than this person, and being that "Family" and "Mindfulness" are inextricably linked in their mind, they must reject Mindfulness because it's tarnished by the behavior of its adherents.
So I'd say, don't attack someone who is acting as an evangelist for something, because perhaps they act in good faith. Particularly in HN, this thread is optional for you and me, and so if you feel like it's proseltyzing, just flag it and move on, don't attack a guy because he believes that Emacs and Lisp are the best apps to install on your Linux machine.