I think that the Buddhist understanding of karma isn't quite the same as the one you explained in this comment.
To start, the phrase that 'people are heir to (inherit from) their own karma or their own actions' appears frequently in the suttas; for example:
Taking responsibility for one's actions
"'I am the owner of my actions (kamma), heir to my actions, born of my actions, related through my actions, and have my actions as my arbitrator. Whatever I do, for good or for evil, to that will I fall heir'...
So far as I know, this doctrine has two consequences:
- It encourages (or justifies, gives reasons for) "right effort" -- e.g. 'I should make an effort because I will inherit the result'
- It permits or helps to maintain "equanimity" (which is one of the brahmaviharas)
Secondly, karma is not the only reason why things happen.
Thirdly I think that your karma affects how you react to things -- for details see the video described in this answer -- for example:
- When you meet someone, if you are heir to good karma (e.g. because you have trained yourself to be kind) then you will, you can, you are able to choose to, act with kindness towards them, with compassion, with equanimity -- and I think this kind of behaviour is described as godly or enlightened.
- Conversely if you are heir to bad karma, then perhaps you have, and you don't control, you can't control, your 'evil' impulses, and so you end up killing them (and then blaming them) -- and I think this is the kind of reason for which you'd be described as being reborn as an animal, or in hell.
You were saying that if you meet someone with bad karma then killing them is unavoidable -- but if a person with bad karma meets the Buddha, for example, I don't see it as possible that the Buddha would be unable to avoid killing them.
Fourthly there's quite a famous exposition of karma e.g. in the Bhagavad Gita. It's been a long time since I read it (and in translation), please forgive me if I misinterpret it -- I might have a very naive or superficial view of it -- but I remember it as being something like (my paraphrase):
A warrior before a battle sees his kin on the other side, and talks to God. God (i.e. Krishna) replies that:
- It's his karmic duty to be a warrior (e.g. because he was born into the warrior caste)
- Killing people is therefore his duty to God -- "selfless service", says Wikipedia
- The people he kills, being mortal, are obviously going to die one way or another anyway
- Fullfiling your duty to God is good karma, not bad karma
Perhaps your view of karma ("killing is unavoidable" and "it's the karma of the victims") has been informed by this kind of doctrine.
I personally see this as quite antithetical to Buddhism, i.e. a way in which the "Buddhist" and the "Hindu" doctrines on karma are quite different, contradictory. I think the Buddhist view is that:
- There's no God (more particularly, perhaps there are Gods but there's no "duty to God" and no "God's laws"); but there is good and evil; and killing people is evil
- Being born into a particular social caste is not a good reason to kill, either
Fifthly, the precise working of karma are complicated -- so complicated that the Buddha's being able to see/understand it as a supernatural power of his -- but I'm not sure it's useful to ask, "for what karmic reason did such-and-such happen?"
I only find a very very simple version of karma to be useful as a theory, e.g. "what you train for, what you practice, you become" and "actions have consequences".
That may be the opposite of the message you were suggesting, e.g. "my actions don't (or shouldn't) matter", "my reaction (e.g. to kill someone I meet) is unavoidable", and "everything is predetermined (by past karma)".
if it isn't true then it seems karma is illogical or there is an element of randomness i.e good karma isn't reliable
Yes there's a limit to how much good karma you accrue. For example with a lot of good karma you may be reborn in heaven, but even then your stay in heaven is temporary (you're reborn when the fruit of good karma is exhausted).
So good karma isn't going to stop you from dying and so on.
I do think that good karma (or a lack of bad karma) might be enough to keep you from killing, though.
I think the "randomness" you mention is a description of the (complicated) circumstances which surround us. The Buddhist definition of karma is that it's "intentional action" -- our actions and reactions -- and that might be less random: a "good" person might for example successfully train themselves to avoid (to refrain from) ever murdering someone, no matter who they meet.