If the Resurrection had not occurred, why would the apostle Paul give such a list of supposed eyewitnesses? He would immediately lose all credibility with his Corinthian readers by lying so blatantly.
Most relativists believe that relativism is absolutely true and that everyone should be a relativist. Therin lies the self-destructive nature of relativism. The relativist stands on the pinnacle of an absolute truth and wants to relativize everything else.