I voted your comment down for two reasons. The first is this:

Another topic that comes to mind is parenting. I'm not familiar with the self-help literature in this area, but there are some quite ugly truths which I'd bet these books don't say, for example how depressingly little you can do beyond the limits imposed by heredity.

Making sweeping statements about a subject with which you are admittedly unfamiliar seems like the sort of thing this community should discourage.

And in this particular case, I think you would be surprised. Parents come up against the limits of their power very, very early on, and modern parenting books are actually very forthright about it. Of course they try and put it nicely -- generally something like "You can't make a sweetpea into an azalea, but with good watering and fertile soil you can help your little sprout become the very best sweetpea he or she can be" -- but the message of being unable to push your child beyond the limits of their own aptitudes is made quite clearly and quite often.

The other reason I downvoted your comment was this:

Some other examples I can think of are too sensitive and potentially offensive to describe with a few casual words, so I'll stop at this for now.

This just seems unnecessarily coy. My guess is that you're talking about HBD, but I think you should either make your case or not bring it up at all.

I'm relatively new here and still learning the ropes--are comments explaining downvotes considered useful? I know I'd appreciate explanations when I get downvoted, but I don't know if others have the same preferences.