Here's one drawback: migratory bird populations collapse, leading to an insect they previously ate having a population explosion, leading to swarms of insects t

Here's one drawback: migratory bird populations collapse, leading to an insect they previously ate having a population explosion, leading to swarms of insects that destroy crops, thus marginally raising food prices and leading to 2M deaths from malnourishment. This isn't even a particularly implausible outcome.