I'll go a more direct route:

The next time you are in a queue with strangers, imagine the two people behind you (that you haven't met before and don't expect to meet again and didn't really interact with much at all, but they are /concrete/). Put them on one track in the trolley problem, and one of the people that you know and care about on the other track.

If you prefer to save two strangers to one tribesman, you are different enough from me that we will have trouble talking about the subject, and you will probably find me to be a morally horrible person in hypothetical situations.