So, why is man intrinsically stupid and runs himself down? Well, it's possibly because we often let our instinctive drives and emotions guide us instead of making rational decisions. We tend to succumb to short-term temptations and indulge in long-term harmful behaviors, such as overeating, smoking, drinking, or shopping addictions.
In addition, we as humanity have often exploited the planet and our resources in the past, rather than acting sustainably and responsibly. We've gotten ourselves embroiled in social and political conflicts, and we're not always able to effect positive long-term change.
But hey, maybe we do have some positive qualities, like creativity and empathy. And who knows, maybe in the future we'll behave more wisely and responsibly and live up to our full potential as a species. Until then, though, maybe we should look at our stupidity with a little humor and self-irony.
Why am I telling or writing this here? No idea, because I can maybe?