"We can't ever know anything enough to do anything" isn't a very useful way to go about the world. The same vague, dark hinting can be applied in the other direction - perhaps there are consequences from introducing Aedes aegypti into the Americas via the slave trade we'll resolve by eradicating the invasive species.
Phrases like "near zero consequences" usually implicitly refer to the consequences for human populations, domestic animals, or species that have cultural value to us or are canaries in coal mines (i.e. polar bears).
As long as the macro-ecological systems we rely on continue to interface with us in mostly the same way we make the compromise that we are aware enough of the side effects. It's easier to take this perspective with disease carrying mosquitos because of the sheer quantity of human suffering and death they cause.
But this view does have pitfalls, like how we initially missed the collapse of pollinator species that we depend on, or the risks we take with genetically cloned fruit like Cavendish bananas which are a single pathogen away from being wiped out.
