best way to look at it is Eric wanted to kill people, but not be locked away by pea-brained law enforcers and Dylan wanted to die, and both of those came together, Eric killed and Dylan died, they both got what they wanted and Eric died and Dylan killed, they both did what the other one wanted.
Maybe Eric felt like he would rather have been born a lion, he would have felt free and been able to hunt, fight to survive, death around every corner, sleep with one eye open, kill or be killed, mate with females without worrying about finding someone who fits with you and all the other natural tasks and he felt that humans aren't free and their life style has been artificially changed and he looked at animals and how we are supposed to be living and he didn't want to be apart of this fantasy life that humans have modified over the centuries. Jobs, marriage, studying, working out and making yourself better to be 'worthy' enough for others to accept you, he felt that that was all bullshit and he just wanted to do what creatures were put on this world to do, what he felt humans are supposed to be doing.
"If it moves.. kill it.. if it doesn't.. burn it.. follow your animal instincts"
"Give the Earth back to the animals, they deserve it infinitely more than we do"
"The human race sucks. human nature is smuthered out by society, jobs and work and school. instincts are deleted by laws."
"Drop all your beliefs and views and ideas that have been burned into your head and try to think about why your here"
"The few people who stick to their natural instincts are casted out as psychos or immature or strangers or just plain different. crazy, strange, weird, wild, these words are not bad or degrading"
"Survival of the fittest, I want to put everyone in an ultimate Doom test, whoever can survive does, whoever doesn't.. doesn't"