If they're outside, whatever. If they're on my house, I destroy the webs, rarely ever kill the spider because they're hiding in the day time. If they're in my house, they trespassed into my realm and their lives are forfeit. It's not like there aren't millions upon millions more of them outside. For me this is true of any insect (and yes I know that spiders are arachnids...). It comes into my house, it is my mission to destroy it.