Are you familiar with the idea of parallel universes?
Yes, at one point I had this mega fascination with that concept, and I happened to be doing my philosophy course in college. Parallel universii and the "flame concept" of human awareness pretty much sums up my view of how "everything" works.
When you light a candle, you see the flame burning. But flames aren't really "things", they're a process. The flame is actually a chain reaction as the molecules oxidize rapidly, this process is the flame, but the actual parts of the flame (molecules) are different every second yet we STILL conceptualize it as a single thing.
In kind of the same way, humans are "processes" and not things. The body that is "me" today isn't the same as the one when I was a 2 year old. My brain isn't the same, my experiences not the same yet I can still use the pronoun "I" without causing my brain to collapse in confusion.
In essence, I believe that at "the moment of creation" (however you define it) all possible universes, as well as all possible moments in "time" are created and exist as snapshots forever still. It is not the "passage of time" that's happening per se, but our awareness moving from one snapshot to another. When we imagine, we're simply viewing "snapshots" from another universe/time and when we "remember" we're simply looking back to a different snapshot.
But here's the thing. If that's true, it doesn't matter because I am still "me" and confined to the track of my thoughts. Perhaps making one choice allows the other choice the shift into another universe or progression, but since I am trapped by this universe (and presumably, everyone else in this universe) it doesn't matter. It's incidentally why I rejected the notion of God. I hold open the possibility that there is a God, but it's clear he's not interacting with the world and that he's decreed that humans are unable to detect him/it. Because of this, true or not, it's entirely irrelevant.
If you think about it this way, then Ian's decisions can't possibly go against another's ambitions, because both Ian and the other person will soon part in parallel universes.
And if you think about it this way, you can kill someone because there exists a theoretical person who was not killed. I'm not calling or implying that either your or Ian are or will be killers but this is the extreme progression of the idea. If a person doesn't limit someone's options because those options exist in some theoretical universe then what's wrong with government or violence (but I repeat myself)? Either you recognize that there is a single universe, in which you are responsible for your actions, or you recognize there are multiple universes and the existence of them are entirely irrelevant in every way which matters to your life.