I don't know, what are the possible effects of antibiotics? What are the possible effects of uprooting weeds, which some organisms may depend on? What are the possible harmful effects of putting out wildfires?
For every action that someone might think of as beneficial, there are all sorts of "harmful" effects that can be posited. In the examples above, these harms are not even just theoretical, and yet people do not constantly wring their hands worrying about wildfire fighting, weed control, or the proper use of antibiotics.
That this seems to happen only with mosquitoes seems quite weird to me, especially when it occurs even with efforts to reduce mosquitoes that spread malaria and other diseases. People are oddly very worried about some nebulous harm caused by reducing real and serious harm now.