This is why stupid idiots shouldn’t be given any power.
Humans constitute .01% of all life on earth by biomass. If he was halving all life instead of all sapient life then nothing would have happened but anticlimatic confusion. though that would be hilarious. Your gut bacteria outnumber the cells that compose you. let alone the ones in the environment.
He wanted to balance out the planet
He used the Soul Stone to make the connection, IIRC, so maybe they just don’t have souls?