The poison is death, because the creature is bound to die. It benefits from its own demise. In every aspect, this is bound to end up in death, because its overall effect suits death. When you are benefitting from the destruction of your own creatures, that is Death. When you are hurting your opponent in equivalence to your own creatures suffering, that is Death. When there is no chance for your creature to avoid this without some kind of HP buff, that is Death. This light isn't purifying you, it's killing you. A mini-rage pot is indeed useful, and the cost decrease would be justified, but the fact remains that Light doesn't suit this at all, except for your vague reasoning.