In Halloween 6 they tried to give him a reason; Michael has been marked with a runic symbol called Thorn, an ancient Druid curse that drives a young man to wipe out his entire family for the good of civilization. In the remake he had a bad childhood, and really only loved his mother and baby Laurie and wanted to be reunited with her until she hurt him. The Thorn storyline is ignored in H20 and HR so like the original and Halloween II he doesn't have a reason for wanting to kill Laurie, he's back to being evil.
At the end of Rob Zombie's Halloween 2, 2009 she was in a psychiatric hospital, there's so many version of the ending, 1 where she picks up the knife and gets shot, and the one where she slowly walks out, kneels down and puts his mask on and kneels.
The say, pure evil....which in a way is true, but the crappy childhood, abusive step dad, bullies at school, a sister who'd rather have sex with her boyfriend than pay attention to her own family, is enough to turn any good guy bad.