Even if we make the extremely conservative assumption that their deaths are only one 600,000th as bad, in terms of suffering, as humans deaths, insect suffering is still obviously the worst thing in the world.
But you pulled the number 600000 out of thin air.
People, when asked to name a small number or a large number, will usually name numbers within a certain range, and think “well, that number sounds good to me”. That doesn’t mean that the number really is small or large enough. It may be in normal situations--$600000 can buy a lot—but if you try to do calculations with it, the fact that people name numbers in certain ranges lets you manipulate the result by starting from a “conservative” number and coming to an absurd conclusion.
If it was, oh, 10000000000000000000000 instead, your conclusion would be very different. The fact that not many people will pick 10000000000000000000000, and that you can conclude insect suffering is important based on 600000, says more about how people pick numbers than it does about insect suffering.
People will pay as much to save 2,000 birds as 20,000 and 200,000 birds.
When you ask the question “what would you pay to save 2000 birds”, the fact that your question contains the number 2000 is information about how many birds it is important and/or possible to save. If you ask the question with different numbers, each version of the question provides different information, and therefore should produce inconsistent answers (unless it’s a poll question specifically designed to test different numbers, but most people won’t take that into account).
I support putting bank robbers in jail. Yet I refuse to support anything that would put myself in jail. I’m clearly supporting it in an imbalanced way that is beneficial to myself.