[He Rides A White Horse]

They probably aren't a risk to humans since most people who do this sort of thing draw a line between human and animal

You are dead wrong. There is a very strong association between torturing animals and serial killing.

They often 'graduate' to killing humans.

[RobRoy]

They often 'graduate' to killing humans.

You're right of course, but the qualifying word in your sentence is "often." If you used the word "always," and I agreed with the use of that word, my position on this would do a 180.