That it will use any excuse to kill people

Religion ... pure and faultless is this: to help widows and orphans in need and avoiding worldly corruption. James 1:27

2000 years religion has taught that it is about helping widows and orphans while avoiding worldly corruption, but for 2000 years no one has learned much.

Rhetorical question? What is humanity capable of learning? And when has humanity EVER responded monolithically, or for that matter retained what was supposedly learned.

I suppose it has taught some of humans to never ever to trust authority merely by virtue of it being authority. But it has taught this through endless examples of duping the public, by promising and then betraying trust. Humanity, for its part keeps showing itself deeply gullible, never everybody in the same way, but virtually everybody in a variety of ways.

Every other thing that I can think of, is just a sub-set of gullibility.

The trouble is that we have a huge range of technologies, language, media and arts, which are able to generate falsehoods far beyond the natural levels of deception that any animal would encounter in nature, so we have no evolved defenses, against the effects of culture as a whole not just religion.