When you have reckless people attacking the elderly you need better psychological healthcare and a better social system to prevent that.
I understand your point and in a narrow context it's definitely true, but in a larger context you can prevent most violence by changing society.
Something like this: https://www.youtube.com/watch?v=2pLb_uc0bo8
Most people doing evil things are in part doing these evil things as a result of their circumstances. By changing their circumstances through social programs you reduce violence and make everyone happier as a result.
You can argue that blaming violence on circumstances ignores people's own responsibility, but I believe that better social and medical programs are still worth it because they attack the part of the root cause society can influence most easily.
There's a variety of reasons for this, but one of 'em is that in a condition of systemic governance, there's some societal pressure against the kind of sadism you mention. In a world like Sparta, it's hard to tell the heroes from the villains, and anybody might lash out at any time. Even the quotes given, spell out situations where random violence was just a part of everyday, expected life. This causes tensions and grudges.