The reason we have these eradication programs is actually predominantly because the flies are harmful to farmed animals. However, they have little or no negative impact on the environment when eradicated. This not only affects wildlife (whose suffering I think should absolutely be considered if we can determine it won’t have knock-on effects), but it also affects humans in impoverished areas. While animals eating other animals is almost always excruciating and fucked up, a screwworm infestation means you get eaten alive over days in basically constant pain, at which point the wound is now susceptible to secondary bacterial infection and death. The world currently spends a bunch of money keeping them contained (and trying to push them further south), and getting rid of them altogether would mean not needing to spend in perpetuity.