Facepalm

I think that's a bit unfair. Frankenstein had no sympathy for his creation whatsoever, he ran away after creation and when he first met him he called him monster and wouldn't listen to his story. The creature had to watch humans from afar and to learn to live, being secluded in a hut for at least a year.

He wanted to bring joy to the family which he called protectors, he helped them when they couldn't see them and was constantly afraid of being discovered. It took him so much courage to confront the family for which he gained affection only to be attacked and they fled quickly after.

In his final speech of the book, his sentiment is basically that. All his life he wanted to converse with other humans and be included in society, but he was not allowed, because everyone called him a monster and screamed at his appearance.

Of course murdering other people was the wrong approach to this situation, but he was equipped with weapons and used them when his emotions were too strong for rationale.