Spiritually speaking, is it illogical to assert the nonexistence of unicorns?

Considering that there's no evidence against unicorns. Some claim that because that there's no evidence of unicorns, that means it is logical to assert the nonexistence of unicorns but, lack of evidence for the existence of unicorns isn't any evidence against the nonexistence of unicorns.Therefor it is illogical to assert the nonexistence of unicorn.......therefor I'm illogical.