What is more terrifying?

There are soulless people, which means there can also be demons with souls.

Yes. Unfortunately, such creatures ("soulless people") do exist. And they are easy to identify. They try their best to make life miserable for people with Souls out of envy and hatred, even without gaining any benefit from it, even to their own detriment. But, I don't have any information about demons having souls. Therefore, I question their existence. And even if such beings could exist, they are either extremely rare or located on some distant, extremely inaccessible plane. So, it's easier to assume that they don't exist.