Please let's get some of the facts straight.
The daddy longlegs that is also known as the harvestman has no venom glands. And it is not a true spider, but it is an arachnid. The most venomous is just a myth. Although some large tropical species might bite a person, there will be no effect because they have no venom whatsoever. They are completely harmless to humans. They are omnivorous feeding on small insects, plants, fungi, and they are also scavengers feeding on decompose matter.
The daddy longlegs spider, although it does have venom, their venom is to weak to have any serious effect on humans. Like all spiders they are beneficial by feeding on insects, such as flies and mosquitos.
The daddy longlegs that is also known as the crane fly is a food source for many birds or any other insect eating animals.
So, whether you like them or hate them, they are just like any creature on earth. They were put here for a reason. They do have their part in the ecosystem, either as predator, prey or scavengers. Just because they may not serve purpose to us, doesn't mean they don't serve a purpose in the ecosystem.