This is what I know:
According to Buddhism, all intentional killing is wrong/ unwholesome. Intentional means desiring death to happen and causing it somehow (even by advice), and it is not the same as motivation, a killing can be intentional or intentional, and intentional killing can be motivated by this or that motivation, e.g. by anger, greed, compassion, etc. All intentional killing is unwholesome regardless of the motivation.
Unintentional killing is not unwholesome, even though it can be a consequence of some unwholesome act. But if someone unintentionally kills someone by doing someone that is not unwholesome, he has done nothing unwholesome, e.g. if one drops a brick or throws a rock without intending to kill or harm anyone, yet someone gets hit by the brick/ rock and dies, the person that has dropped/ thrown it has not done anything unwholesome.
Even if a killing is done unintentionally by doing an unwholesome act the killing itself isn't unwholesome, being that it wasn't intentional. The example given in the Tipitaka is a monk hitting another monk out of anger, which is an offense. So, if a monk hits another monk out of anger without the intention of killing him, but the monk that was hit dies from the blow, the monk that hit him hasn't committed the offense of killing but the offense of hitting a monk out of anger.
The rule mentioning the offense (Pc 74) is interesting, because commentary on it allows self-defense, of course, as long as there's no intention to kill. Thanissaro Bhikkhu, in his explanation of the Buddhist Monastic Code elaborates on that rule (like on all the other rules, including the first precept [listed Pj 3] from where I got the above information about Buddha's view on killing) and as the section "Non-offenses" gives this passage as explanation:
"According to the Vibhaṅga, there is no offense for a bhikkhu who, trapped in a difficult situation, gives a blow "desiring freedom." The Commentary's discussion of this point shows that it includes what we at present would call self-defense; and the Commentary's analysis of the factors of the offense here shows that even if anger or displeasure arises in one's mind in cases like this, there is no penalty."
What I've been thinking about and what about I want to ask is this:
When ten unwholesome conducts are enumerated, it is not just killing that is named as the first bodily one, but "Here someone is a killer of living beings, he is murderous, bloody-handed, given to blows and violence, and merciless to all living beings." Blows and violence are, together with killing, named as the first bodily unwholesome conduct.
In the light of such enumeration, is there any explanation in the Tipitaka or early literature as to why is violence that lacks the intention to kill given leeway if it has a proper motivation, whereas the one that includes it isn't, even if it has the same motivation as the former?