Entities were the primary reason I ceased DMT and have no interest in psychedelics anymore. Wasn't scarred or anything but I realised that I don't understand the mechanics, no one does, and the risks outweigh the reward - once I became convinced these entities are not purely imagination then I had no choice but to stop. That is not to say that 'positive thinking', trip setting, and other methods don't work in ameliorating a bad experience in progress.. it just doesn't change the fact these entities can have their own independent essence from yours. They may not actually look that horrific or anything like how our minds perceive them, I suspect that is the case, but the non-beneficial or mutually beneficial intent is evidently missing from their presence.
I get the light/dark 'all is within us' aspect, at the highest level that may be true - I think it is. However, at the physiological and mental levels that wisdom may not offer any protection at all. There may be laws and mechanics involved that we can't see or understand in relation to entities. Can they latch on to the body-mind somehow, infiltrate the mind or become embedded in the thought processes? No one knows for certain, that's one of the risk-rewards you have to weigh up in the end.