And live your life forever an amnesiac with only a part of your personality and being? Plus several of them were causing trouble that he had to stop anyway. The only reason Visas screwed up is that he hunted his other counterparts in the wrong order. Should have merged with the Mannadium counterpart, who represented his good ego and was the only one fine with merging before going after all his darker aspects. Scareclaw counterpart representing fear and instinct, Tearlaments representing despair, and the Kashitra one which finally overtook him with its unbridled rage. So the Mannadium fought him and than merged with him to balance out all the evil in Visas to save him