Can I use these both?
It's a product of a diseased mind.
It's a product of a sick mind.

Question

Answer

Yes, but there is a nuanced difference.   “Diseased mind” suggests there is some mental illness, and that you are not saying that the person in question is morally to blame.   “Sick mind” suggests that the person in question is just an evil, twisted, cruel person, and that he is morally to blame for his bad actions.