When it comes to the whole monitoring felons, I really don't have anything to make an educated suggestion about it. I do have an idealistic stand on it, where the felon would be able to rehabilitate itself and be a productive member of society. If you can't lock 'em for life and you can't kill, and decide to release the person, you're gonna need to something to help him maintain somewhat of a healthy life. This is really waay above me and I really can't come up with a solution for this type of shit.
As for the second part of course what one sees/hear constantly will have an impact on their behaviour and on the mindset of things. It's absolutely ridiculous to say that an individual that continuously enjoys music that promotes violence, enjoys video games that promote violence, watch movies that promote violence, listen to his political leaders spew bullshit about more violence and war on this and that, won't be effected by any of it. Some would be able to resist the constant bombardment of such negativity while others are mentally more fragile and are more susceptible indulge in the activities that their favorite rapper promotes.