1) Species (and groups of species) do not exist just in order to serve or please human beings. Human beings are not the only important thing in the world. Do you really think you, and your own (not undestructive, and often very unattractive) species are that special and important? Get over yourself!
2) Wasps are (mostly) predators, and predators exist in ecosystems to keep them in balance so they are not swamped by writhing hordes of prey. A world without wasps would be a world with an inconveniently large number of aphids and caterpillars.
3) Wasps pollinate plants. When did YOU last pollinate something? Well, there you go.
4) Wasps have bright, sharp colours, clean lines: they are fast, deadly, tough hunters that don't take kindly to being messed about with and can look after themselves. They are not teetotal, and you'd better not annoy them. Wasps are awesome.