I'm much more puzzled by the many retorts to people asking about the unforeseen consequences of eradicating a whole species given how little we know about ecosystems.
Many such comments are very dumb, asking 'and how do you feel about viruses, screwworms, etc.?', but since you say this is a genuine question: mosquitoes are numerous and we know that they represent a source of food for many species (bats, birds, other insects). As far as I know, there is genuine debate among scientists about the role that mosquitoes play in their ecosystems. Everyone here has seen species of animals and plants eradicated and then being reintroduced or replaced, when we realise what role they were playing.
Again, assuming you're asking in good faith: you're asking why these commenters are so concerned while humanity is eradicating species all the time anyway: these are not the same populations... I'd wager there is a big overlap between those wondering about consequences and those taking action for the planet (not eating animal products, not flying, etc.). Similarly, I'd wager there's overlap between those posting such illogical retorts, and those eating animals at every meal and driving their car daily.
I see the same ridiculous retorts in HN debates about the condition of animals.
Okay, but we aren't talking about the eradication of all mosquitos. Approximately 10% of known mosquito species are potential carriers of human disease (https://entomologytoday.org/2022/07/26/less-than-10-percent-...), and discussions about eradication efforts generally revolve around just the Anopheles genus.
There's an excellent book on the impact of the mosquito on humanity, and a brief overview of some of that subject here: https://www.newyorker.com/magazine/2019/08/05/how-mosquitoes.... These species of mosquito are and have been one of the most significant threats to human health for all of our existence.
I don't think argument-from-ignorance should be more convincing here than it would be on any other subject. There is some debate among researchers, sure, but published biologists have been making arguments in favor of eradication for over 20 years (https://www.nytimes.com/2003/09/25/opinion/a-bug-s-death.htm...). If someone is being intellectually honest in objecting to this on the grounds of the fragility of ecosystems, then they must also be an equally loud voice against the use and manufacture of glyphosate. That one chemical alone is already having a far greater impact on insect populations, yet you can buy it at your local hardware stores.
So yeah, I genuinely don't understand the reasoning here. It feels like a dumber version of the trolley problem, where a perceived inaction that has far larger negative consequences is preferable to an action with more limited ones -- except in this case, it's not even right to describe our current impacts on ecosystems as "inaction".
I suspect that if an article were published tomorrow that found that, through some previously-unknown mechanism, the expected rise in global temperatures over the next 10 years would have a side-effect of killing all mosquito populations, that article wouldn't even make the front page of HN. Nobody much would care, aside from those few recurring voices mourning our future.
More cynically, I also suspect that since the worst impacts on human health are occurring in tropical populations, westerners find it much easier to argue in favor of protecting this particular pest.