We definitely don’t know for sure, but we absolutely know the harm caused by malaria and dengue. (I personally care about this from living in places with both, and because Elon Musk almost died from dengue, apparently.)

Everyone almost died of a lot of things. We're all lucky to be alive. For people in countries with Malaria, its like the flu. In fact, flu also kills a lot of people.

What's the solution to diseases? Improving peoples' general health and wellbeing, so that their immune systems can handle the disease. The solution is not to eradicate an entire species in the middle of an already distraught global ecological catastrophe.

For every instance of a mosquito causing a malarial infection, there are likely uncountable instances of mosquitoes causing inoculation.