I didnt mean you have to have mental issues to do drugs…but think of it this way there are people out there with mental issues that would never do a terrible thing like that unless they were all jacked up on drugs. I think of it almost like a synergy effect…a person on drugs only may not do a thing like that, a person with mental issues and not on drugs may not do a thing like that…but that same person with the mental issues who is all hopped up on drugs may do something like that. I see your point about logical thought but I think drugs can alter what you think is logical.
To sum it all up:
Drugs only = may do bad things
Mental issues = better chance to do bad things
Drugs + mental issues = Best chance to do bad things