I'm in favor of wiping out mosquitoes, but I think people are generally more concerned about _disrupting_ the ecosystem; not outright collapse. You're right that it's unlikely wiping out any one particular species would collapse any ecosystem. But it can certainly cause dramatic shifts in ecosystems, which people generally don't want.
For example, we recently re-introduced wolves into Yellowstone park. It was done because previously we had wiped out the wolf population, and we're now trying to re-establish it (we did a lot of bad things to Yellowstone historically, but luckily we've spent the past decade or so rebuilding it. The bison are thriving again!).
But, for economic reasons, we used the wrong wolves; cheaper wolves (seriously). Well ... that hasn't gone well at all. They've started wiping out other species in the park, and now that the park is bereft of other large game, the wolves are going after the bison. The bison we _just_ re-established. Luckily the bison are very robust and difficult beasts to hunt, but that doesn't help the fact that the other species have been decimated.
Has the Yellowstone ecosystem collapsed? No. But it has changed; changed by introducing just one species. And the change is quite dramatic.
For example, we recently re-introduced wolves into Yellowstone park. It was done because previously we had wiped out the wolf population, and we're now trying to re-establish it (we did a lot of bad things to Yellowstone historically, but luckily we've spent the past decade or so rebuilding it. The bison are thriving again!).
But, for economic reasons, we used the wrong wolves; cheaper wolves (seriously). Well ... that hasn't gone well at all. They've started wiping out other species in the park, and now that the park is bereft of other large game, the wolves are going after the bison. The bison we _just_ re-established. Luckily the bison are very robust and difficult beasts to hunt, but that doesn't help the fact that the other species have been decimated.
Has the Yellowstone ecosystem collapsed? No. But it has changed; changed by introducing just one species. And the change is quite dramatic.
Oops.