Provide some quotes from Frankenstein that support and some that do not support the statement, "No one is completely good or completely evil."

The duality of man is an overarching theme in Frankenstein and with it comes the nature of good and evil. Some of the best quotes addressing this theme come not from Victor but from the monster himself. When the monster finds out how Victor truly felt after his creation, he laments his condition and likens it to that of Satan in Paradise Lost. The monster then laments:
"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. Satan had his companions, fellow devils, to admire and encourage him, but I am solitary and abhorred."
For those familiar with the biblical references, they will note that Satan, a former angel, was made beautifully in God's image but still chose to pursue wrongdoing. The monster on the other hand was deformed and hated by his creator, yet up until this point he only sought to understand and be understood.
Throughout the work Victor assumes the monster is evil based merely on appearances yet the monster proves by his efforts that is not the case. Even when he commits terrible acts, he feels remorse. Thus disproving the evil is inherent or that only those who do not fit societal standards on beauty are automatically evil.

One of the most striking elements about Frankenstein is that neither Frankenstein nor the Creature are purely good or evil characters.
The most significant quote dealing with this idea comes from the Creature himself:

I do know that for the sympathy of one living being, I would make peace with all. I have love in me the likes of which you can scarcely imagine and rage the likes of which you would not believe. If I cannot satisfy the one, I will indulge the other.

Here, the Creature claims he was not born wicked. He is like any other human being: capable of good and evil with his upbringing and environment having a great impact on which path he will be willing to take.
Frankenstein himself takes the opposite approach, at least at the beginning. When he looks upon his Creature after it comes to life, he says this:

I beheld the wretch—the miserable monster whom I had created.

He calls the Creature, barely a few minutes into life, miserable. He assumes that just because the Creature is ghastly to look upon that he must be evil on the inside as well. However, Mary Shelley seems to put more stock into the idea that no one is all good or all evil.