>I'm actually very interested in hearing concrete ideas of what the unintended consequences could be and their cost, from actual experts.

Not all unintended consequences can be predicted let alone have a cost attached to them. In fact by definition unintended consequences are those we cannot forsee or prepare for in any meaningful way. Of course virtually any action has some unintended consequences but I think what the naysayers are saying in this case is that with something as complicated and untested as this, there is potential for massively negative unpredictable outcomes (maybe a new invasive species, maybe aedes aegypti perform some as yet unknown ecological function and their loss would be massively detrimental in ways we can't as yet predict etc), and there's some justification for that from human experience. This was the entire premise for movies like Jurassic park