(Including me).
I’ve noticed that “most” people (no, no cite I can give you, I’m using my anecdotal life experience) won’t kill ladybugs in instances that if it were any other bug, they’d be deadskies.
In fact, a lot of people seem to react quite positively to seeing a ladybug.
What gives?
Don’t they eat other bugs? Kind of a natural pesticide.
And they’re cute.
Because they kill other insects. Nothing ladylike about em. I prefer to have a pest free garden.
They’re one of the few bugs that gets to live if it happens into my home. They don’t bite, they don’t fly around and get in your face or buzz around lights, they’re little and kind of cute. No reason to kill them, really.
Ladybugs eat aphids. But I think it’s because it’s not one of the bugs we are trained to fear as children. Spider=kill! Bees=Kill! Flies=Og SMASH! But for ladybugs, we teach children a little rhyme.
Possibly because of the centuries old cultural meme that pretty = good and ugly = bad?
If you smoosh them they leave a red stain and that sucks.
I think some varieties of ladybug (or bugs that look an awful lot like ladybugs) stink if you smoosh them, but don’t quote me on that. And no I don’t mean stinkbugs.
And yes, good at eating other bugs.
Cute factor, of course.
Flies don’t have a cute factor. They get killed. Scorpions don’t get a cute factor. They get killed, and often tortured to death. Spiders, no cute factor: they get killed, except for people from countries where they’re seen as beneficial to human health because they kill mosquitos which transmit deadly diseases. Bees and wasps pose a problem: on one hand they are kind’a cute, on the other teaching kids (and stupid, uninformed grown-ups) how to tell them apart and that it’s a Bad Idea to try and smoosh one because that is when they bite has been known to cause some serious fights.
Ladybugs and escarabajos de san antonio (I don’t know what are they called in English, they’re the multi-segmented black ones that form a ball when poked) are cute and don’t bite, so it’s as if they have a Do Not Kill sign.
There’s a relatively recent invasive species to the US that looks like an orange ladybug - they do bite, and they stink if squashed. I think I’ve heard them called “Asian ladybugs.”
But yeah, same reason why people don’t kill butterflies: they’re pretty and don’t bite. Plus that whole aphid-eating thing.
Note to anybody googling: I find images for “vaquitas de san antonio” which are ladybugs, the bugs I know as escarabajos de san antonio are completely different - but still cute. Heck, they’re used as a jewelry motif!
Those are the worst - the first few summers they showed up, I would be so happy, because Ladybugs are great!!1!
Then I got bit by one, and now I am death on Ladybugs. You can’t swat them because of the hard shells and the bite factor, and if you smash them, they stink in an Old-Lady, dead flower sort of way. Can’t vacuum them either, because your vacuum will then send that stink all over. We scoop them in toilet paper and flush them.
For the record, I don’t kill spiders unless they’re on my face or something. If I get one on my arm, I’ll flick it off, but never smash.
My mother and grandmother told me it was good luck to find a ladybug, particularly in the house. It would be cruel (and probably bad karma) to kill something that just brought me luck 
As well as all the other reason, superstition - it’s bad luck to kill a ladybird/bug.
They stain and they stink.
I don’t know how wide-spread this is, but when I were a lad we were told that very tiny spiders were “money spiders” and that if you could keep one on your hand for [some period of time that I’ve forgotten– probably a minute] it brought good luck and you would soon come into some money. And, of course, there was “Incey Wincey (or Itsy Bitsy) Spider”.
So small spiders, good – large spiders, bad, apparently.
I don’t kill any bugs. Except one that attacks me and tries to take my blood. Why should I?
I mentioned that on the superstitions thread the other day too - let the money spider run across your palm and you’ll get money. Spiders are much cuter or at least less creepy the smaller they are, when you can’t see those eyes and pincers.
Ladybugs are cute, to me at least. And we BUY ladybugs, so that they will eat aphids.
Death to Asian ladybeetles, though. They’re cute, but they’re a pest.
They significantly reduce the aphid population, among others. Most nurseries sell bags of ladybugs to release among your plants. It’s quite a sight to see them swarm up a tree from where you’ve released them; it must be like what the Mongol hordes looked like to the rest of Asia.