What makes a monster? A monster makes itself. A person will not be considered a monster if they are kind, gentle and warm hearted. You've never heard a person say, "Gandhi was a monster," or "Mother Theresa was a monster." You could hear someone jokingly call a tall or large person a monster just because of his or her size.
Society can also make a monster. As you saw in Frankenstein, if the monster had a normal body or a normal look to him, he wouldn't have been rejected, which, in turn, he wouldn't have killed all those people he did. In the book, the monster is rejected outright of love and compassion. His sheer size and look frightens people, and not understanding that even though he looks the way he does he still just wants to be loved like everyone else. Like most people, if you are rejected you feel either sad or angry, and when you are always being rejected, it's hard to bear.
If the monster in Frankenstein had sat at home and wallowed in it's self pity, we the readers, would feel sympathetic towards the monster, but it would have made a boring read...although it's boring enough as it is. Even though he killed all of those people, we still felt a sense of pity or understanding towards the monster. We understand that everyone needs love and compassion. Now a days can understand that there are other things that are important than just your looks, although some people can find that hard to believe.
We can compare the monster in Frankenstein and other monsters we have come to learn of. The number one point is that the monsters looks are something we aren't familiar with, or don't understand. Most Sci-Fi movies have the alien as...