Why would victor Frankenstein rather than his creation most likely be considered a monstrous?

Because he is obsessed with creating a living being. APEX

He would be considered monstrous rather his creation because he went against the social norms for that time period and tampered with life and death. By bringing life to something that shouldn't be alive, it is seen as an evil act or the conjuring dark magic. The unknown is a delicate subject that will cause the most innocent people to turn against those among their communities.