Conclusion
While Kevin's speech was quite vulgar, and watching him as he spoke indicated all the great intensity of the violence that was in him, he was still intelligent enough to realize where his motivations were coming from.
He did indeed look like a savage animal about to pounce at any second, with the slightest provocation.
But once he was given healthy outlets for all that energy like athletics and workshops he began to quiet down. And being away from a sick environment he began to build some self-esteem.