Why do you not believe in God?

[Skepsis]

Reason 1. God is an unverifiable idea: There’s no concise definition of god, so a god can be anything that believers want it to be. This means that the definition of god can change to evade falsification. For example, when Darwin discovered that species are created by natural selection, rather than the God of Genesis, the definition of the Biblical God changed. No one today worships natural selection, even though it’s the actual mechanism responsible for the creation of new species. However, people do continue to believe in the Biblical God. The fact that the definition of god can change prevents us from ever verifying a god's existence.

I don't think I quite follow the reasoning here.

Our understanding of the laws of nature have changed over time. We went from the Greek notion of the four elements to the periodic table, from aether to atoms, and so on and so forth.

Each time, a previous conception was proved to be false in some way. Similarly, a previous conception of God was proved to be false in some way. That doesn't mean you can't verify God's existence (although modern science is based on falsification, not verification), it just means you're verifying that lots of different conceptions of god are false. Maybe eventually they'll all be shown to be false?

You know why those Gods are now regarded as fairy tales by the general populous? When previously unfalsifiable propositions can be tested, they lose their validity. Why?
Nearly every claim ever made that couldn't be falsified had no basis in the beginning, and only hid under their shroud of unfalsifiability to cease scrutiny. When it turned out that our universe behaved in different ways than we had previously understood, the set-in-stone definitions were already too concrete to be altered and thus fell to the axe of science.
So many Gods fell to new descovery, so much so that Gods are scared of discovery. Quantum theory is scaring apologists right now with the idea of particles that can freely come into being without cause.