Agreed for villianizing mosquitoes though
So the horses that were released (and have thrived!) in north america are originally north american horses. It's part of why they do so well-- they can eat all of the native brush here. Whereas if a cow gets loose in n. america it's gonna poison itself.
https://awionline.org/content/wild-horses-native-north-ameri...
https://returntofreedom.org/new-research-proves-yet-again-th...
That is to say, their natural predators are either not present, not present in large enough numbers, or forbidden by law to hunt them.[0]
I believe the word you are looking for is extirpated. They didn't go extinct, they just aren't there anymore.
> Don’t we need a grazing species in these areas?
Suppose that depends on your idea of what those areas should be doing.