Are wasps pest or are they good for the environment?

Wasps are much maligned. They are a gardener's friend, and a short life history may explain why.
In spring a queen wasp comes out of hibernation. She searches for a suitable place to start a nest and lay eggs. During this time she feeds on nectar from flowers, so at this stage she is a pollinator. Although the adult wasp lives on nectar or similar sugary sources, the larvae are carniverous, so the queen (and later, the worker wasps as they emerge) capture caterpillers and other insects, including a lot of garden pests, to take back to the nest for the larvae to feed on. In return, the larvae produce a sweet, sugary substance rather like honeydew and the adult wasps feed on this. During this time you are probably not too aware of the wasps around you.
At the end of summer the queen lays eggs for drones (males) and new queens. When they emerge as adults they will fly off and mate. The old queen then stops laying. The problem for the wasps now is: no eggs means no larvae; no larvae means no honeydew. The wasps have lost their food supply. This is when they turn to the ripening fruit and other sources of sugar -- and people see them as a pest.
As the colder weather comes, the new queens find somewhere sheltered in which to to hibernate, but all of the other wasps die.
Overall, they do far more good than they do harm.