Because it's a freaking SPIDER.
It HAS to die, regardless of what it did.
But, that's so racist. A race never deserves to die. Not only does it mess up the ecosystem, it's just plain mean. If I went around and killed every spider, we'd have a huge increase in the fly and mosquito population, for one thing, which would not be good. For another, people would probably give me a bad rap. And, finally, that would so decrease the tourist industry, with corpses everywhere
In all seriousness, though, killing things just because of their race is not a good thing.
But honestly, does anybody like spiders? Or insects and arachnids?
I mean, all they do practically is just crawl around, mess up food and bother you. Especially flies, which pretty much do nothing but fly.