The Vortigaunt are actually a very misunderstood race of alien invaders. Under mind control by The Nihilanth, a powerful alien that mentally enslaved the Vortigaunt as well as other races, they were used to attempt to destroy the world.
As shown in Half-Life 2, while not under mind-control, the Vortigaunt are peaceful and ritualistic. They have been seen as healers. In fact, when gathered in a large group they can heal others quite quickly. They also use the same power to shoot bolts of energy at enemies and create localized shock waves. They became allies to the planet's inhabitants after the invasion and release from mind control.
It says something when the species that invades wants to help, especially if they feel remorse after causing so much harm in the first place. I could see the Vortigaunt arriving to help us and enrich our culture more than causing us problems.