Of course Buddhism has no mandatory beliefs but if you drop reincarnation and keep karma you are left with asking where all that karma that determines your life comes from if not a previous life.
From the actions of other people? One part of Buddhism is to de-emphasize the concept of 'self', so the difference between "good/bad actions will cause good/bad things to happen to future reincarnations of me" and "good/bad actions will cause good/bad things to happen to other people in the future" might be smaller than it would seem at first sight.
One part of Buddhism is to de-emphasize the concept of 'self'
Buddhism does not de-emphasize "self" to focus on other people.
Buddhism de-empahsizes "self" in the meaning of the continuity of identity -- the classic Buddhist view looks at the mind/soul as beads on a string (of time) -- the beads are similar but they are not just one bead.
I'm afraid I haven't properly designed the Muggles Studies course I introduced at my local Harry Potter fan club. Last Sunday we finally had our second class (after wasted months of insistence and delays), and I introduced some very basic descriptions of common biases, while of course emphasizing the need to detect them in ourselves before trying to detect them in other people. At some point, which I didn't completely notice, the discussion changed from an explanation of the attribution bias into a series of multicultural examples in favor of moral relativity. I honestly don't know how that happened, but as more and more attendants voiced their comments, I started to fear someone would irreversibly damage the lessons I was trying to teach. They basically stopped short of calling the scientific method a cultural construct, at which point I'm sure I would have snapped. I don't know what to make of this. Some part of me tries to encourage me and make me put more effort into showing these people the need for more reductionism in their worldview, but another part of me just wants to give them up as hopeless postmodernists. What should I do?