The air bender genocide was done by the earth kingdom.
Think about it; no fire damage to any of the temples, the fire nation failed to get through a WOODEN door, and the whole thing was up on some mountains, the fire nation didn’t have the tech back then.

You know who did? The dai li. Walking up stone faces is their most well known skill, they use deception constantly, and earth bending would make more sense for the damage done.

Sozin’s perspective of the temple burning down made no sense, there wasn’t any fire damage after it was destroyed, and there were BRIDGES between the parts of the temple, which weren’t there later on. His memory was faulty, and WHO is skilled with brainwashing? Those weren’t firebending soldiers, just bodies in the uniform.

After the “fire nation” attacked the air temple, it was the earth kingdom and water tribes that declared war. Air and earth are opposites. What if, wanting to maintain greater control of their kingdom without interference, the dai li wiped out the airbenders, who embodied the ideals of freedom, then framed the fire nation, their next largest threat?

The fire nation was innocent