[kbenson]

I wouldn't call them arbitrary. As a society we've chosen to make the idea of helping the less able lead more normal lives something we want. Whether it really helps or is the most effective way is debatable, but I think it's pretty clear why; it's generally well supported and fits with our cultural mythos.

[soup10]

Also young people don't vote ;)

[kbenson]

Yes, I also thought of that as well. :) I didn't feel like exploring how that interrelates to other classes like the disabled in complex ways though[1], so omitted it.

Edit: s/included that as well/thought of that as well/

1: Do the disabled benefit from this association and the voting power of the elderly, and if so how much of our cultural wish to help the disabled is rationalization after the fact?