The first piece of evidence for this is biographical. Some critics suggest that Mary Shelley's husband, Percy Bysshe Shelley, was actually the model for Victor Frankenstein, something substantiated by the subtitle The Modern Prometheus, which might be read an an allusion to Percy's verse drama "Prometheus Unbound." Percy was a brilliant poet, but shared the arrogance of Victor. Shelley had begun his relationship with Mary while he was still married to another woman, and was prone to adultery. Like Percy, Victor is handsome, brilliant, and self-centered, from a distinguished upper-class family, with a habit of acting on impulse and not considering the consequences of his actions.
The monster points out that he is, in a sense, Victor's child, and Victor is, in every sense, a terrible father. The monster describes reading Victor's notes about his creation and comments:
'Hateful day when I received life!' I exclaimed in agony. `Accursed creator! Why did you form a monster so hideous that even YOU turned from me in disgust? God, in pity, made man beautiful and alluring, after his own image; but my form is a filthy type of yours, more horrid even from the very resemblance.'
Imagine that the monster is like a child with special needs. A good parent has the capacity to love children who might have various disabilities or unusual appearances; most of us would consider it morally reprehensible for a parent to hate a child with Down's syndrome or some other inherited condition that makes the child appear unusual, and yet here Victor is disgusted with a shape he himself had deliberately created in its original form.
Victor lets Justine be hanged for a murder committed by the monster. This again shows him as irresponsible, and mainly concerned with his own position and reputation rather than with other people.
When the monster begs for a bride, Victor again acts out of self-interest and revulsion rather than realizing, as the monster explains, that what creates the monster's character is, in fact, the way Victor treats him. Just as abused children can grow up to become abusers, so the monster's creator, Victor, is actually a model of self-interest and obsessive pursuit of selfish goals rather than someone who contributes to society and is kind and loving to his offspring, and thus a bad role model for his creation.